Download Level 2 Biology - Learning on the Loop

Level 2
Biology
Revision Guide
Contents
Content ......................................................................................................................................................... 2
Cell Structure and Function .......................................................................................................................... 3
Genetics ...................................................................................................................................................... 17
Ecology ........................................................................................................................................................ 23
Biology 2.8 Describe cell structure and function (3 credits)
Subject content
Types of Cell
o
Animal Cells
o
Plant Cells
o
Bacteria Cells
o
Protist Cells
o
Unicellular Fungi
Cell Organelles
o
Cell Wall
o
Cell Membrane
o
Cytoplasm
o
Nuclear Membrane
o
Nucleus
o
Chromosomes
o
Mitochondria
o
Chloroplasts
o
Centriole
o
Cilia
o
Flagellum
o
Vacuole
o
Contractile Vacuole
o
Ribosome
o
Endoplasmic Reticulum
o
Lysosome
o
Golgi Apparatus
o
Eye Spot
Diffusion
o
Structures involved in Diffusion
o
Process of Diffusion
o
Function of Diffusion
o
Factors that influence Diffusion
Osmosis
o
Structures involved in Osmosis
o
Process of Osmosis
o
Function of Osmosis
o
Factors that influence Osmosis
o
Factors influencing cell structure
Active Transport
o
Structures involved in Active Transport
o
Process of Active Transport
o
Function of Active Transport
o
Factors that influence Active Transport
Secretion
o
Structures involved in Secretion
o
Process of Secretion
Respiration
o
Structures involved in Respiration
o
Process of Respiration
o
Fermentation
o
Function of Respiration
o
Factors that influence Respiration
Photosynthesis
o
Structures involved in Photosynthesis
o
Process of Photosynthesis
o
Function of Photosynthesis
o
Factors that influence Photosynthesis
DNA Replication
o
Structures involved in DNA Replication
o
Process of DNA Replication
o
Function of DNA Replication
o
Factors that influence DNA Replication
Enzymes
o
Enzyme Structure
o
Enzyme Function
o
Factors that influence Enzymes
Achievement criteria
Achievement
Describe cell structure and function.
Make sure you can:
Describe aspects of biology relating to cellular components, organelles, and cellular processes
at appropriate points
Interpret information in a table
Draw accurate, labeled diagrams.
Achievement with Merit
Explain cell structure and function.
Make sure you can:
Meet criteria outlined for Achievement
Accurately use key biological terms in explanation
Explain how or why something happens by linking cause and effect in answer
Draw accurate, labeled, and annotated diagrams.
Achievement with Excellence
Discuss cell structure and function.
Make sure you can:
Meet criteria for Achievement and Merit
Link answers in paragraphs, clearly showing in your
components/organelles and cellular processes
discussion the links between
Apply biological ideas and show evidence of logical thought processes in answers.
Types of Cells
Animal Cells:
Note – Chromosomes are contained on the nucleus, vacuole may
also be present in animal cells. See plant cell below.
Plant Cells:
Note – Plasma membrane is the cell membrane and the nuclear
envelope is the nuclear membrane. Chromosomes are found in the
nucleus.
Bacteria Cells:
Note – Nucleoid is the region where a single chromosome is located.
Cytoplasmic membrane is the cell membrane.
Protist Cells:
The anatomy of protist cells vary. They are unicellular eukaryotes, and may contain an eye spot, cilia and a contractile vacuole.
Amoeba
Euglena
Unicellular Fungi:
Yeast cells are the only type of unicellular fungi used in exams.
Paramecium
Cell Organelles
Cell Wall:
Structure: Semi-rigid structure outside the cell membrane. The cell wall is made of cellulose.
Function: Keeps the structure of the cell and limits its volume.
Cell Membrane:
Structure: Membrane surrounding the cell and inclosing the cell organelles (excluding the cell membrane). The cell membrane
consists of a double layer of lipids.
Function: Controls the movement of substances into and out of the cell. The cell membrane is involved in secretion, diffusion,
osmosis and active transport.
Cytoplasm:
Structure: A watery solution containing dissolved substances, enzymes and cell organelles.
Function: The cytoplasm is the site of translation in a cell.
Nuclear Membrane:
Structure: Membrane surrounding the nucleus. The Nuclear membrane consists of a double layer of lipids, and has a series of
nuclear pores (penetrated holes).
Function: Protects the genetic material, and controls the passage of genetic information into the cytoplasm. The nuclear
membrane is involved in protein synthesis.
Nucleus:
Structure: Membrane enclosed organelle which contains the cells genetic material and nucleolus. The nucleus is contained in
the cytoplasm.
Function: Regulate the cells genetic material. The nucleus includes the functioning of the nucleolus and the nuclear membrane.
Chromosome:
Structure: Coiled DNA which is wrapped around the protein chromatin. Chromosomes are only formed during DNA replication,
aside from this, DNA exists in long strands.
Function: The genetic material for a cell. Chromosomes are involved in DNA replication.
Mitochondria:
Structure: Organelle bounded by a double membrane within the cytoplasm.
Function: Site of respiration. Convert chemical energy into ATP.
Chloroplast:
Structure: Organelle bounded by a double membrane within the cytoplasm. Chloroplasts contain a green pigment termed
chlorophyll.
Function: Site of photosynthesis. Convert energy from the sun into chemical potential energy for respiration.
Centriole:
Structure: Small, barrel shaped organelles within the cytoplasm. Centrioles consist of a series of microtubules.
Function: Associated with nuclear division/DNA replication.
Cilia:
Structure: long hair-like structures protruding the cell membrane.
Function: Assist the cell in movement.
Flagellum:
Structure: Long hair-like structures protruding the cell membrane.
Function: Assist the cell in movement.
Vacuole:
Structure: Large watery substance surrounded by a double layer of lipids (double layer of fats) within the cytoplasm, usually
filled with an aqueous solution of ions.
Function: Aid the cell in storage, waste disposal and growth. Vacuole is involved in diffusion.
Contractile Vacuole:
Structure: Above structure, but void of ions in solution – ie only filled with water.
Function: Regulate the water concentration of the cell. Contractile vacuole is involved in osmosis.
Ribosome:
Structure: Small structures within the cytoplasm that are made up of RNA and proteins. They may be free within the cytoplasm,
or attached to the rough endoplasmic reticulum.
Function: Involved in the manufacturing of proteins. This process is called biosynthesis, and is the process of converting mRNA
into proteins.
Endoplasmic Reticulum:
Structure: Comprises of a network of tubes and flattened sacs within the cytoplasm. May be rough or smooth, which indicates
whether or not the endoplasmic reticulum has ribosomes attached to it.
Function: Involved in protein synthesis. Proteins are assembled on the ribosomes.
Lysosome:
Structure: Sac bounded by a single membrane from within the cytoplasm which contain enzymes and are pinched off from the
golgi apparatus.
Function: Contain enzymes which are used to break down food and foreign materials
Golgi Apparatus: (also called golgi body)
Structure: A series of flattened disc shaped sacs within the cytoplasm, stacked on top of each other which are connected with
the endoplasmic reticulum.
Function: Stores, modifies and packages proteins.
Eye Spot: (also called stigma)
Structure: Photoreceptive organelle within the cytoplasm. They are composed of photoreceptors, and a signal transduction
system.
Function: Involved in light detection.
Diffusion
Structures involved in Diffusion:
All membrane organelles are involved in diffusion. These include:
-
Cell Membrane.
Nuclear Membrane – therefore also the nucleus.
Membrane of Mitochondria.
Membrane of Chloroplast.
Vacuole.
Contractile Vacuole.
Endoplasmic Reticulum.
Golgi Apparatus.
Process of Diffusion:
Diffusion is the movement of substances across a semi-permeable membrane, from an area of high concentration to an area of
low concentration. Diffusion involves:
-
The movements of substances which follow a concentration gradient – high to low, the higher the gradient, the
faster the process will be.
No energy; therefore, diffusion is passive transport. The process of diffusion is uncontrolled by a cell.
Small molecules.
No carrier molecules.
Function of Diffusion:
Diffusion is used in cells for the absorption of nutrients. Typically involves small molecules such as water, carbon dioxide, ions
and small proteins. Diffusion can also involve carrier systems that do not require energy.
Factors that influence Diffusion:
-
High Pressure of environment (surrounding a cell) increases the speed/kinetic energy of particles increasing the
rate of diffusion through a membrane.
-
High Temperature of environment increases the speed/kinetic energy of particles increasing the rate of diffusion
through a membrane.
-
High Surface area to volume ratio of a cell increases the rate of diffusion compared to the cells necessity level of
substances for call processes, as the amount of essential substances entering the cell compared to the cells
requirements of these substances will be high. As the volume of a cell increase, the surface area to volume ratio
of the cell will decrease, thus, the amount of essential substances entering the cell compared to the cells
requirements of these substances will be low. The amount of essential substances for a cell increases as its
volume increases because the cell organelles will be larger, ergo they will be needing more energy to perform
processes within the organelles, which comes from respiration (needing oxygen from diffusion), which may be
obtaining glucose from photosynthesis (needing carbon dioxide and water from diffusion), thus, the larger the
cells volume, the more substances the cell will need. Can link also with flaccid, turgid properties of a cell. Often
referred to as greatly folded in membranes – means the membrane has a high surface area.
-
High Concentration gradient will increase the rate of diffusion through a cell membrane, as the molecules will
disperse to the region which has a lower concentration of molecules. The higher the concentration gradient, the
faster (greater the rate of diffusion) diffusion will be.
-
High or low pH in the solution surrounding a cell will cause cells membrane to disintegrate. This is because
membranes are made of lipids, and lipids are fats, and fats are esters, and esters form an equilibrium reaction in
either acidic or basic solutions. The equilibrium reaction involves the fat molecules being converted into a
carboxylic acid/carbonyl ion group and an alcohol group. Thus, the membranes will disintegrate, killing the cell
which results in the cell being unable to undergo diffusion.
Diffusion is not influenced by the respiration, photosynthesis, energy of a cell or carrier molecules involving energy (systems).
Osmosis
Structures involved in Osmosis:
-
Cell Membrane.
Vacuole.
Contractile Vacuole.
Process of Osmosis:
Osmosis is the diffusion of water across a semi-permeable membrane, from an area of high concentration of water molecules,
to an area of low concentration of water molecules. Diffusion involves:
-
The movement of water molecules which follow a concentration gradient – high to low, the higher the gradient,
the faster the process will be.
No energy; therefore, osmosis is passive transport. The process of osmosis is uncontrolled by a cell.
Water molecules (which are small).
No carrier molecules.
Function of Osmosis:
Diffusion is used in cells for the absorption of nutrients. Typically involves small molecules such as water, carbon dioxide, ions
and small proteins.
Factors influencing Osmosis:
Osmosis is the diffusion of water. All factors that apply to diffusion (see above) will apply to osmosis.
Factors influencing Cell Structure:
The movement of water in osmosis is caused by a concentration gradient. The tendency of water molecules to follow a
concentration gradient is determined by the water potential of both the system and the surroundings. The water potential of a
system is the ability of a system to lose or gain water molecules by osmosis. The lower the concentration of water molecules in
a system, the lower its water potential (pure water has a water potential of zero, anything less than this will have a negative
water potential).
-
Water diffuses from regions of more negative potential to regions of less negative potential.
When the water potential of the cell is greater than the water potential of the surroundings, the cell will be hypertonic. When
the water potential of the cell is less than the water potential of the surroundings, the cell will be hypotonic.
Active Transport
Structures involved in Active Transport:
-
Cell Membrane.
Nuclear Membrane – therefore also the nucleus.
Membrane of Mitochondria.
Membrane of Chloroplast.
Vacuole.
Contractile Vacuole.
Endoplasmic Reticulum.
Golgi Apparatus.
Process of Active Transport:
Active Transport is the transportation of substances against a concentration gradient through a membrane. Active transport
involves:
-
The movement of substances against a concentration gradient.
Energy – as it is active transport. The process of active transport is controlled by the cell.
Typically involves larger molecules (not always the case ie contractile vacuole facilitating water transport).
Require carrier molecules.
Function of Active Transport:
Active transport is used in cells for the absorption of nutrients, typically involveing larger molecules. Active transport involves
the following:
-
Ion Pumps (facilitated diffusion) are used to control the amount of a certain ion inside a cell.
Exocytosis is used to expel unwanted materials from a cell by fusing vesicles with the cell membrane. Requires
energy to expel contents.
Pinocytosis is used to ingest liquids into a cell. The cell encloses the liquid into a vesicle then ingests the liquid.
Requires energy to form the vesicle.
Phagocytosis is used to ingest solids into a cell. The cell encloses the solid into a vesicle then ingests the solid.
Requires energy to form the vesicle.
The contractile vacuole regulates the water volume within a cell to maintain a constant internal
environment/osmoregulation. The water potential outside cells that have a contractile vacuole is high compared
to the water potential of the cell. If the water volume of the cell reaches a certain point due to the process of
osmosis, the cell will burst. The function of the contractile vacuole is to remove excess water from the cell to
prevent the cell from bursting, and because the water molecules are going against the concentration gradient,
this process is active transport and requires energy.
Factors influencing Active Transport:
-
The energy (ATP) content of the cell will affect the functioning of active transport, as active transport requires
energy.
High Concentrations of the transporting substance will result in a quicker rate of active transport.
Required energy comes from respiration, which requires the diffusion of oxygen. Respiration also requires
enzymes, which are sensitive to heat ect.
Secretion
Structures involved in Secretion:
-
Golgi Apparatus.
Process of Secretion:
The process of secretion involves the storage, modification, and packaging of proteins.
Respiration
Structures involved in Respiration:
-
Cell Membrane.
Mitochondria.
Process of Respiration:
Respiration is the process of converting glucose and oxygen into carbon dioxide, water and energy (ATP). Respiration is
performed in the mitochondria of cells, and requires oxygen which comes from diffusion, first through the cell membrane then
through the membrane of the mitochondria. The chemical reaction of respiration is the following:
C6H12O6 + 6O2
6CO2 + 6H2O + ATP (energy)
Fermentation:
Fermentation is the chemical process of converting glucose to ethanol and carbon dioxide, and is implemented without oxygen.
It is usually done by yeast cells. The chemical reaction of fermentation is the following:
C6H12O6
2CH3CH2OH + 2CO2 + ATP (energy)
Function of Respiration/Fermentation:
Respiration provides energy for all other cell processes. Fermentation is used without the presence of oxygen.
Factors influencing Respiration/Fermentation:
Both the above processes use enzymes to catalyze the reactions. Thus, all the factors that influence enzymes will be passed on
to both the above processes. The more mitochondria in a cell, the more energy the cell will have to perform cell processes.
More active cells need a higher amount of energy, so they need more ATP from respiration, thus they will need/have more
mitochondria for respiration. If the water potential of the solution outside yeast cells is low, the cell will dehydrate, and the
enzyme production will lessen, therefore the production of fermentation will decrease.
Photosynthesis
Structures involved in Photosynthesis:
-
Chloroplasts.
Mitochondria.
Cell Membrane.
Process of Photosynthesis:
Photosynthesis is the process of converting water and carbon dioxide in the presence of sunlight, to glucose (chemical potential
energy) and oxygen. Photosynthesis is performed in the chloroplasts in cells, and requires water and carbon dioxide, which are
obtained by diffusion through the cell membrane, and light energy from the sun. The chemical reaction of photosynthesis is the
following:
6CO2 + 6H2O
LightEnergy
C6H12O6 + 6O2
Function of Photosynthesis:
Photosynthesis results in chemical potential energy (glucose) which can then be converted to energy (ATP) from respiration in
the mitochondria. The ATP energy gained is then used for all cell processes.
Factors influencing Photosynthesis:
The process of photosynthesis requires enzymes, thus all the factors that influence enzymes will consequently affect
photosynthesis. The positioning of the chloroplasts is important. This is because the distance required for carbon dioxide and
water (from diffusion entering through the cell membrane) to travel to the chloroplasts will be less if the chloroplasts are
arranged close to the cell membrane. The numbers of chloroplasts in a cell will affect the amount of glucose produced. Light
intensity will affect the functioning of photosynthesis, as the lighter the surrounding environment, the greater the rate of
photosynthesis. The more chlorophyll in the chloroplasts the more light energy will be absorbed.
DNA Replication
Structures involved in DNA Replication:
-
Nucleus.
Chromosome/genetic material.
Nuclear Membrane.
Process of DNA Replication:
Genetic Material within the nucleus condenses into chromatin, then chromosomes. The double helix strands of DNA split at the
replicating fork into separate strands. Free nucleotides bonds with the two strands creating two daughter DNA strands.
Function of DNA Replication:
DNA Replication occurs during cell replication. Cell replication results in two daughter cells. In a multi-cellular organism, this is
the growth of the organism. In a unicellular organism, it is the propagation of the species.
Factors influencing DNA Replication:
DNA Replication requires enzymes, thus all factors that influence enzymes will inherently influence DNA replication. The cell
must have reached a certain level of maturity before it can replicate successfully.
Enzymes
Enzyme Structure:
Enzymes are globular proteins that contain a series of activation sites which make up a cleft. Enzymes can also undergo the
reverse process of the below process shown. Enzyme structure is important as the active sites are specific to a certain type
substrate/subunits. If the shape of the enzyme is altered, its function will also be hindered (see below for affects). As evidence
add the diagram below to illustrate an answer.
Enzyme Function:
Enzymes are catalysts in biochemical reactions. Substrate/subunit molecules are drawn to the cleft, usually by weak bonds. The
substrate/subunit molecules are fitted into the enzyme in an induced fit; the enzyme changes its shape, and the molecules are
either forced to combine (as with subunits), or they are forced to break apart (as with substrate molecules). They speed up
reactions by lowering the activation energy (creating an alternative pathway for the reaction) required so biochemical reactions
may function at an increased rate. Without enzymes, biochemical reactions would be too slow to support life. Enzymes can be
used multiple times, as they are unchanged during the reaction. If the enzyme shape is altered, the biological reaction will not
be speed up/rate has dropped due to the absence of catalysts (enzymes). The biological process is hindered; therefore overall
functioning of the cell is also hindered (depends upon the biological process involved). Enzymes are used in both respiration
and photosynthesis.
Factors that influence Enzymes:
-
-
Enzymes are temperature specific and have an optimum temperature. At low temperatures, the particles
(Substrate/subunit molecules) will have less kinetic energy, and will form fewer bonds with the activation sites of
the enzymes, so the enzymes will have low activity/low rate of combination for particles. At higher
temperatures, the particles (Substrate/subunit molecules) will have more kinetic energy, and will form more
bonds with the activation sites of the enzymes, so the enzymes will have a higher activity/higher rate of
combination of particles. However, at high temperatures the enzymes will change shape and the enzyme will
denature. At optimum temperature, the particles (Substrate/subunit molecules) will have high kinetic energy,
and will form more bonds with the activation sites of the enzymes without the enzymes shape denaturing.
Enzymes are pH specific and have an optimum pH level. The presence of hydronium ions or hydroxide ions can
alter the shape of the enzyme molecule.
Concentration of substrate/subunit particles will increase the rate of reaction, as more will be attracted to the
enzymes at any one time, so there will be more collisions/bonding of the particles with the enzymes, thus there
will be more activity and the rate of reaction will increase.
Large molecules can inhibit the functionality of enzymes. They are called enzyme inhibitors, and attach
themselves to the activation site of enzymes. This will result in a change in shape of the enzyme, thus the
enzyme will not function correctly.
-
Large molecules can also prohibit the functionality of enzymes. They are called enzyme cofactors, and attach
themselves to the activation site of enzymes. When substrate molecules form weak bonds with the enzyme, the
enzymes can attach themselves to cofactor molecules which will act as a bridge, holding the substrate molecule
to the enzyme.
Biology 2.3 Describe genetic variation and change (3 credits)
Subject content
Inheritance
o
Definition of Inheritance
o
Alleles
o
Genotype
o
Phenotype
o
Dihybrid Cross
o
Test Cross
Genetic Variation
o
Process of Meiosis
o
Independent Assortment
o
Segregation
o
Crossing Over (Recombination)
o
Mutations
o
Factors that influence Genetic Variation
Genetic Change in a Gene Pool
o
Definition of a Gene Pool
o
Natural Selection
o
Migration and Immigration
o
The effect of Mutations on a Gene Pool
o
Genetic Drift
o
Founder effect
o
Bottleneck affect
Achievement criteria
Achievement
Make sure you:
Describe biological concepts and processes that relate to genetic variation and change
Understand that mutation leads to variation
Attempt to use a test cross to determine genotype
Are able to interpret biological graphs
Are precise in your descriptions of relevant terms such as genetic, evolutionary, mutation,
gene pool, alleles, genes, genotype, phenotype, bottleneck effect, genetic diversity, natural
selection, mitosis, and meiosis
Can use Punnett squares to show understanding of biological crosses.
Achievement with Merit
Make sure you can:
Meet the criteria for Achievement
Understand the link between variation and how this affects survival of a population
Explain changes in population due to natural selection and the passing on of genes to
offspring
Demonstrate understanding of a dihybrid cross.
Achievement with Excellence
Make sure you can:
Meet the criteria for Merit
Construct logical and well ordered answers that can expand upon key ideas
Evaluate and discuss reasons for lack of variation in offspring by recognising selection
pressures
Demonstrate an understanding of relevant biological concepts and relate them to unfamiliar
scenarios.
Inheritance
Definition of Inheritance:
Inheritance is the passing of traits from one generation to another.
Alleles:
Alleles are a version of a gene. Chromosomes come in pairs called homologous chromosomes, and on each chromosome there
are versions of genes (alleles). If the two alleles are the same for both homologous chromosomes, the individual will be
homozygous for the subject gene. The combination of two alleles which are both dominant for the subject gene is termed
homozygous dominant. The converse is true for the combination of two alleles that are recessive (ie homozygous recessive). If
the two alleles on homologous chromosomes are different, then the individual will be heterozygous for the subject gene.
Genotype:
The genotype of an individual is the combination of alleles for a particular gene in an individual.
Phenotype:
The phenotype of an individual is the physical characteristics (traits) of the individual.
Dihybrid Cross:
When two individuals are mated, the inheritance patterns of two discontinuous genes can be shown by a Dihybrid cross. The
possible gametes for both genes of the two individuals are shown, and the resultant combinations of all the gametes are
represented on a table. If there are only two possible combinations for one or both the individuals, only these two are shown in
the table. If there are two discontinuous genes; gene A and gene B, and two individuals that are heterozygous for both genes
were mated, the Dihybrid cross would be thus:
Female Gametes:
Male Gametes:
AB
Ab
aB
ab
AB
AABB
AABb
AaBB
AaBb
Ab
AABb
AAbb
AaBb
Aabb
aB
AaBB
AaBb
aaBB
aaBb
ab
AaBb
Aabb
aaBb
aabb
The genotype ratio is the ratio of possible genotype combinations of the offspring of the two individuals. In this case it is:
1:2:2:4:1:2:1:2:1 (AABB:AaBB:AABb:AaBb:AAbb:Aabb:aaBB:aaBb:aabb)
The phenotype ratio is the ratio of possible phenotype combinations of the offspring of the two individuals. In this case it is:
9:3:3:1 (Trait A, Trait B: Trait A, Trait b: Trait a, Trait B: Trait a, Trait b)
Test Cross:
When an individual’s phenotype shows the dominant trait, the individual could he either homozygous dominant or
heterozygous for the trait. The individual’s genotype can be found by breeding the individual with a known homozygous
recessive individual. The phenotypic ratio of the offspring of this cross will be either:
1:1 (Dominant Trait: Recessive Trait)
Or the offspring will all show the dominant trait. If all the offspring show the dominant trait, the tested individual will be
homozygous dominant (see punnet square below for details). If any of the offspring show the recessive trait, the tested
individual will be heterozygous (see punnet square below for details).
The tested individual will have all F1 offspring heterozygous (will all show the dominant trait as phenotype), thus the
individual will be homozygous dominant.
A
A
a
Aa
Aa
a
Aa
Aa
The tested individual will have half F1 offspring showing the dominant trait and half the F1 showing the recessive trait. Thus,
individual will be heterozygous.
A
a
a
Aa
aa
a
Aa
aa
Genetic Variation
Process of Meiosis:
The process of meiosis is split into several steps:
-
DNA replication occurs. The genetic material of the cell is replicated. Gametic mutations may occur at this step.
The chromosomes condense, and the homologous pairs pair up. Crossing over may occur at this stage.
The chromosome pairs line up on the equator of the cell, in a way that is completely random. This process is
called Independent assortment.
The homologous chromosomes separate, and the cell is split into two separate immediate cells.
The two immediate cells divide again into a total of four haploid cells called gametes.
Independent Assortment:
Independent assortment is the idea that two or more pairs of alleles segregate independently of one another during the
formation of gametes. When homologous pairs of chromosomes line up during meiosis, the arrangement is completely
random, so the two chromosomes are randomly distributed. This leads to different combinations of chromosomes in daughter
cells. Independent assortment will therefore lead to genetic variation in the gametes produced in meiosis, and genetic variation
in the resultant individual (offspring).
Segregation:
Segregation is the idea that members of each pair of alleles on different homozygous chromosomes, separate to different
gametes. The separation of alleles will produce different allele combinations in the gametes. Segregation will therefore lead to
genetic variation in the resultant individual (offspring).
Crossing Over (Recombination):
Crossing over is the exchange in segments of chromosome between homologous pairs during meiosis. The result of this process
is the recombination of genetic material on homologous chromosomes. Crossing over leads to the genetic variation in the
resultant individual (offspring).
Mutations:
Mutations may come in two different forms:
-
Gametic mutations – A gametic mutation is a mutation that occurs in the gametes (ie during meiosis – see
above). Only mutations that affect the gametes can be inherited by an individual.
-
Somatic mutations – A somatic mutation is a mutation that occurs after fertilization (ie after meiosis – caused by
mitosis after fertilization). These mutations will not be inherited (won’t be present in all the individuals body
cells), but can affect the individual.
Factors that influence Genetic Diversity:
All the above factors influence the genetic diversity, and lead to a great genetic variation in offspring.
Genetic Change in a Gene Pool
Definition of a Gene Pool:
A gene pool is all the alleles in a population.
Natural Selection:
Natural selection is the change in allele frequency within a gene pool due to an environmental pressure. The environmental
pressure/change will favor a certain phenotype in the population. The individuals within the population that show the
phenotype that is more suited to the change in environment will have a higher chance of reproducing (because they will stay
alive). The individuals that do not show the phenotype that is more suited to the environmental change will have a lower
chance of survival. The better suited individuals will pass there genetics on to further generations by inheritance, and the
favored alleles will have a high chance of being obtained by these individuals. Individuals that do not suit the environmental
change will have a lower chance of passing on their genetics to further generations. Thus, natural selection results in the
change in the allele frequency within a gene pool.
Immigration and Emigration:
Immigration is the movement of individuals from another population into the population. The alleles of the immigrated
individual will be added to the gene pool of the population. Emigration is when individuals leave the population. The alleles of
the emigrated individual will be lost from the gene pool. Both the above processes result in the change in the allele frequency
of the gene pool.
The effect of Mutations on a Gene Pool:
A mutation is a permanent change in the genome of an individual. All new alleles derive from mutations, thus mutations are the
source of all new genes. For a mutation to become established in the gene pool, the mutation must have occurred in the
gametes (gametic mutation). Mutations can result in new combinations of amino acids; therefore they can also result in new
alleles in the gene pool. If the new allele(s) are better suited to the environment, the allele frequency of the population can be
changed by natural selection.
Genetic Drift:
Genetic Drift is the changing in the allele frequency of a population due to chance. In small populations, the gene pool will be
small, and alterations in the allele frequency due to genetic drift can have a large impact on the gene pool. This results in the
loss of alleles of small gene pools. In large gene pools, the alterations in the allele frequency due to genetic drift will have a
smaller impact on the gene pool. Depending on the size of the gene pool, alleles will have a lower chance of being lost in larger
populations.
Founder effect:
The Founder effect is when a small group become isolated from a larger population and establishes a new population. Due to
the small gene pool of the new population, the allele frequency may not be representative of the original population. The
founder effect results in the genetic change in a gene pool, because the isolated environment may differ from the original
environment, resulting in the smaller population evolving differently from the larger population (due to natural selection and
genetic drift).
Bottleneck effect:
A population bottleneck is a significant reduction in the size of a population, possible due to an environmental change. The
reduced population will be smaller than the original population; therefore alleles may become lost from the population. If the
reduced population reestablishes itself, there will be little genetic diversity in the species, because all future generations have
propagated from the smaller population (which had a small gene pool due to small numbers). If a future environmental change
is to occur, it can have a detrimental impact on the population because there is little genetic diversity in the gene pool – ie
individuals will have similar genetics and few will be favored with the environmental change (natural selection will not favor
certain individuals). Typically, there is little time for mutations to occur in the population to give rise to new and possible better
alleles (increase genetic diversity), this is why the population will have little genetic diversity to begin with. This will result in the
genetic change in the gene pool due to the lack of genetic diversity compared to the original population.
Biology 2.5 Describe the concepts and processes relating to
ecology (3 credits)
Subject content
Ecosystem
o
Definition of an Ecosystem
o
Definition of a Community
o
Definition of a Population
o
Definition of a Community
o
Definition of a Specie
o
Food Chains
o
Food Webs
Environment
o
Abiotic Factors
o
Biotic Factors
Ecological Niche
o
Definition of Ecological Niche
o
Aspects of an Ecological Niche
o
Habitat Preference
Trophic Relationships
o
Trophic Levels
o
Producer
o
Consumer
Biodiversity
o
Definition of Biodiversity
o
Biodiversity Alterations on an Ecosystem
Adaptations
o
Definition of an Adaptation
o
Structural Adaptation
o
Physiological Adaptation
o
Behavioral Adaptation
Ecological Pyramids
o
Pyramids of Number
o
Pyramids of Biomass
o
Pyramids of Age
o
Age Structure
o
Energy Pyramids
o
Flow of Energy
o
Growth Rates
Ecological Features
o
Succession
o
Zonation
o
Stratification
o
Distribution and Density
Symbiosis Relationships
o
Competition
o
Exploitation
o
Commensalism
o
Amensalism
o
Mutualism
o
Antibiosis
o
Overview of Symbiotic Relationships
Nutrient Cycles
o
Nitrogen Cycle
o
Carbon Cycle
Achievement criteria
Achievement
Make sure you can:
Recognise and name ecological relationships or patterns
Accurately define ecological terms
Read and interpret biological graphs.
Achievement with Merit
Make sure you can:
Meet the criteria for Achievement
Compare and contrast biological concepts and processes to support statements
Use annotated diagrams to support explanations
Use your own words to explain an ecological concept or process.
Achievement with Excellence
Make sure you can:
Meet criteria for Merit
Compare and contrast using relevant examples to support statements
Combine information provided by resource material with own knowledge to discuss ecological
concepts
Use annotated diagrams to support discussions
Construct an answer in a clear and logical fashion.
Ecosystem
Definition of an Ecosystem:
An ecosystem is made up of all the communities in an area, and there physical environment.
Definition of a Community:
A community is all the populations within a defined area between which there is a defined flow of materials. If a ecosystem has
great variety and has a large amount of communities, it will be more stable.
Definition of a Population:
A population is a group of individuals of the same species living in one area, at the same time.
Definition of Specie:
All the organisms, that can breed with each other to produce viable (alive and able to reproduce) offspring.
Food Chains:
A food chain is the chain of organisms in a community through which food and energy flow. Arrows point in the direction of
flow of the energy. Each link in a food chain represents a trophic level. Many food chains usually exist within a community.
Species often belong to more than one food chain, and may occupy different trophic levels in different chains.
Food Webs:
A food web will consist of all the food chains in a community. Arrows point in the direction of flow of energy.
Environment
Abiotic Factors:
The abiotic factors in an environment are the physical (non-living) factors of the environment. Abiotic factors include:
-
Temperature.
Soil type (pH, nutrient levels).
Pressure (Altitude levels, oxygen affects).
Light (Intensity, direction and wavelength).
Water (Salinity, humidity and pH).
Wind (speed, direction and exposure).
Biotic Factors:
The biotic factors in an environment are the living factors of the environment. Biotic factors include:
-
Competition.
Predation.
Parasitism.
Mutualism.
Density.
Ecological Niche
Definition of Ecological Niche:
An ecological niche of an organism is its role in a community. Gause’s principle states that “No two species can have the same
ecological niche in the same habitat for an indefinite period of time”. Two species can co-exist if they have different ecological
niches. Two or more organisms can be proven to have different ecological niches, by knowing that the two (or more) species
can continue to occupy the same ecological niche and survive.
Aspects of an Ecological Niche:
There are several aspects of the niche of an organism. These include:
-
The Habitat of the organism. This is the place where the organism lives.
Feeding level. This is the trophic level that the organism operates on.
Adaptations. The behavioral and structural adaptations of the organism, that allows the organism to live
successfully.
Life History. This indicates the life stage the organism occupies. At different periods, an organisms role will
change, the history of the organism shows the current niche of the organism.
Habitat Preference:
The Habitat preference of a species is self-explanatory. It is the habitat that an organism that is best suited to.
Trophic Relationships
Trophic Levels:
Each link in a food chain represents a different trophic level. A species can occupy more than one trophic level, as they can have
multiple sources of food. Trophic levels represent the feeding level of a species.
Producer:
Producers (or autotrophs) make their own food source by photosynthesis. Producers are influenced by the following abiotic
factors:
-
Light intensity.
Hazardous environmental conditions (ie – wind, rain ect).
Oxygen levels.
Water levels.
All food sources derive from producers in food webs. Producers occupy the first trophic level. Producers gain energy from:
-
The sun (ie light energy).
Producers lose energy from:
-
Respiration.
Growth and new offspring.
Being eaten by consumers.
Wastes (metabolic wastes are released).
Reflected light.
-
Death (to decomposers).
Consumer:
Consumers (heterotrophs) obtain their food source by consuming other organisms. There are many types of consumer. These
include:
-
Primary Consumers (herbivores), obtain their food source by eating plant material.
Secondary Consumers (carnivores), obtain their food source by eating primary consumers.
Tertiary Consumers feed on secondary consumers.
Predators obtain their food by killing and eating their prey.
Scavenges obtain their food by eating material left by predators, or animals that have died from disease or
injury.
Parasites feed off other living organisms.
Omnivores feed off both plant and animal matter; therefore belong to both secondary and primary consumer
classes.
Organisms may belong to any of the above groups (ie more than one group). Consumers gain energy from:
-
Food: by feeding off other organisms.
Consumers lose energy from:
-
Respiration.
Growth and offspring.
Eaten by carnivores.
Metabolic wastes.
Death (to decomposers).
Biodiversity
Definition of Biodiversity:
Biodiversity is the diversity of life within an ecosystem.
Biodiversity Alterations on an Ecosystem:
If a species is wiped from a community, all other species that feed on that species will be adversely affected. If there are any
species that only feed on the species wiped from the community, they will either be wiped out or must adapt and/or change
habitat. If the species wiped is a producer, the entire food web of a community may be affected, due to all food sources
deriving from producers (photosynthesis).
Adaptations
Definition of an Adaptation:
Adaptations are inherited characteristics which enable organisms to survive or reproduce more effectively. There are two types
of adaptations; Structural adaptations, or behavioral adaptations.
Structural Adaptation:
Structural adaptations are adaptations involving special parts of an individual’s body. Structural adaptations may include:
-
Wings, for flight and also helps an individual avoid predators.
Beak, protection, breaking shells (hard substances) for food (food source) ect.
Claws, protection – as above for beak.
Prickles on bushes, discourage predators eating the bush.
Physiological Adaptation:
Physiological adaptations are systems within an individual’s body that allow it to perform certain biochemical reactions.
Physiological adaptations may include:
-
Enzymes which catalyze biochemical reactions.
Positioning of organ systems.
Warm-bloodedness.
Mitochondria.
Behavioral Adaptation:
Behavioral adaptations are adaptations pertaining the way a species lives. Behavioral adaptations may include:
-
Feeding times (nocturnal, diurnal), avoid feeding at same time as predators ect.
Sleeping times, as above.
Mating calls.
Hibernation.
Ecological Pyramids
Pyramids of Number:
Pyramids of number show the amount of individuals present for each species in a food chain. The individual of the highest
trophic level will be shown at the top, and the individual of the lowest trophic level will be at the bottom.
Pyramids of Biomass:
Pyramids of biomass show the mass of each species at each trophic level in a food chain. In most cases, the lower levels will be
much larger than the higher levels. This is because most of the energy obtained from feeding ect, will be converted into heat
and other forms of energy, as well as keeping bodily functions operating. This will result in less energy being passed on to
subsequent trophic levels; therefore less mass will be present in these levels. The mass of each species at each trophic level
includes the mass of skeletons ect – therefore pyramids of biomass are not fully representative of the energy levels of each
species at each trophic level.
Pyramids of Age:
Age pyramids show the relative number of organisms present at particular age groups of a population. They are used to show
whether a population is increasing or decreasing (or staying constant). The width of the pyramid will show how many
individuals are at each stage.
Age Structure:
For a population to grow:
-
The amount of births per unit time must exceed the amount of deaths in the same time interval. The death rate
is termed mortality, whereas the birth rate is termed natality.
At each age group in a species, there may be different amounts of
individuals dying. The probability of individuals dying at any age group can
be shown on a survivorship curve.
In humans, the mortality rate is low until old age. In coral, mortality is
constant. In plants, mortality rate is high until old age.
Energy Pyramids:
Energy pyramids show the energy flow from one trophic level to another in a food chain. The width of each level is dependent
on the amount of energy in each trophic level. Energy is lost at each level due to energy transformations, thus each higher level
will be smaller than the level below it. Energy pyramids look very similar to pyramids of biomass (see above).
Flow of Energy:
Energy is lost at each level because of energy transformations. The flow of energy through an ecosystem can be shown by the
following:
-
Light energy is gained by producers (approx 2%), and is used to convert water and carbon dioxide to glucose and
oxygen. Energy is lost by cell processes such as respiration.
Primary consumers (herbivores) feed on the plant tissue (approx 20%), and use it for respiration and other cell
processes.
Secondary consumers feed on the primary consumers (approx 10%), and use it for respiration and other cell
processes.
This process continues in this trend, where energy is lost in each trophic level. 98% of the original light energy is reflected back
into space, and energy is lost in each trophic level as heat from respiration and other cell processes. Eventually, all energy is lost
as heat radiated back into space. Nutrients however must be continually recycled. Food chains with only a few trophic levels
will have more energy at the top trophic level than those that have high amounts of trophic levels. This is because at each
trophic level approximately 90% of the energy will be lost to respiration ect.
Growth Rates:
The growth rate of a population is the rate at which the population is growing (ie natality vs mortality).
The following graph shows the growth rate of cells. From 0 – 40 time units, the
graph shows an increase in population numbers (natality is greater than mortality
rates. From 40 – 80 time units, the graph shows that the population is neither
increasing nor decreasing (natality is equal to mortality – stable population). At 80
– 120 time units, the graph is gradually decreasing (mortality is greater than
natality rates).
Ecological Features
Succession:
Ecological succession is the process by which communities in a particular area change over time. Succession is the result of
many changes in the abiotic and biotic factors that exist in an ecosystem. Basically, communities alter the abiotic factors in an
environment to suit their preferred niche. The change in abiotic factors allows different species to inhabit the change in
ecosystem, resulting in a change in the communities present in the ecosystem. This in turn affects the abiotic factors, and thus
the biotic factors also, and so on. Primary succession involves:
-
The new establishment of a community, where there were no other communities present. This will result in an
ecosystem, as there are now both abiotic and biotic factors in the environment.
The newly established community will change the abiotic factors to suit its preferred niche, thus allowing the
community to change.
When the ecosystem reaches a stable state (ie one that is constant – not changing), the community present is
called the climax community.
Secondary succession involves:
-
The event of a catastrophe that alters the biotic factors within an ecosystem. This will change the abiotic factors
also.
The change in abiotic factors will change the community within the ecosystem.
Once the original community is established (assuming the previous community was at climax community status),
the community will be a climax community.
Zonation:
Zonation refers to the gradual change in gradient of an environmental factor. For each species, there is a range of tolerances for
which that species can survive in. As environmental conditions exceed the tolerance limits for a species, the species will no
longer be able to survive. Different species are more tolerant to certain environments than others.
Stratification:
Stratification is a pattern in the types of vegetation present at each vertical layer of a forest community. The forest is divided
into five separate layers. These are:
-
Canopy, which is the highest layer.
Sub canopy, which is below the canopy.
Tree fern layer.
Shrub layer.
Ground layer.
The following abiotic factors affect plants in a forest community:
-
-
Light intensity: The higher plants (ie those in the canopy and sub canopy) will obtain more light than those in
lower layers. Higher level plants will block out the light from the species below, thus the plants at lower levels
will live in a darker environment.
Humidity: The lower environments will have higher humidity levels. The cover provided by the higher plants
restricts the air movement at lower levels, thus the environment at lower levels will be more humid.
Temperature: Greater range in higher levels, smaller range in lower levels.
Wind: Air movement is greater at higher levels.
Shelter is given to plants in the lower environments, so they will not be exposed to heavy rain and violent winds ect, which
could damage them. Species that live in each layer will be adapted for the layer which they live. Adaptations include:
-
Species lower in the forest will be more adapted to lower light intensity (leaves larger and greener), and unable
to survive in places with higher light intensities.
Species lower in the forest will also be more adapted to higher humidity levels, and will have a narrower
tolerance range for temperature levels compared to the plants in higher levels.
Species lower in the forest will have lower air movement, so will disperse seeds another way aside from wind
dispersal.
Distribution and Density:
Both the distribution and density are properties of populations.
-
Population density is the number of individuals per unit area.
Population distribution is the way that population numbers are distributed, and is usually described as a
distribution pattern.
There are two density types for a given population:
-
Low density: Where there are low numbers of individuals present per unit area.
High density: Where there are high numbers of individuals present per unit area.
There are three distribution types for a given population:
-
Random distribution: Individuals are randomly dispersed around an area.
Clumped distribution: Individuals conform to groups.
Uniform distribution: Individuals are dispersed in equal intervals between each other.
Symbiosis Relationships
Competition:
Competition is the interrelationship where species or individuals are competing for the same resource, with both parties
suffering. There are two types of competition:
-
Intra specific competition: When there is competition between individuals from the same species. Intra specific
competition for resources increases with increasing population size. When the demand for a specific resource
exceeds the supply, the resource becomes a limiting factor. The result of a limiting factor is the reduction in
population size (ie from lowering the natality rate of the population). Different species have different responses
to limited resources.
-
Inter specific competition: When there is competition between individuals from different species. This is usually
less intense than intra specific competition, because different species usually adapt to occupy different niches,
thus they will have different resource requirements.
Exploitation:
Exploitation is the interrelationship where one species benefits at the expense of another species. Exploitation includes:
-
Predation: Predation occurs when one individual hunts and kills another individual (prey) as a food source.
Predators do not usually control the numbers of the prey species that they feed on.
Herbivory: Herbivores do not usually kill the plant that they are feeding on.
Parasitism: Where one species obtains nutrients from another without killing its host.
Commensalism:
Commensalism is the interrelationship where one species benefits from the presence of another species, where the other
species is neither harmed nor benefited by the relationship.
Amensalism:
Amensalism is the interrelationship where one species is harmed by the presence of another species, where the other species is
neither harmed nor benefited by the relationship.
Mutualism:
Mutualism is the relationship where two species benefit from the others presence. Mutualism does not involve conscious
cooperation of either species, as each species acts only in its own interest.
Antibiosis:
Antibiosis occurs when one species benefits (or is unharmed), by producing a compound (ie a poison, antibiotic) which inhibits
the growth of another organism.
Overview of Symbiotic relationships:
Type of Interaction:
Species A:
Species B:
Competition
Harmed
Harmed
Exploitation
Harmed
Benefits
Commensalism
Not Affected
Benefits
Amensalism
Not Affected
Harmed
Mutualism
Benefits
Antibiosis
Benefits or Not Affected
Benefits
Harmed
Nutrient Cycles
Nitrogen Cycle:
Nitrogen is an essential element for living things for the following reasons:
-
Nitrogen is needed in proteins. As all living things need proteins (enzymes to catalyze cell processes), therefore
all living things also need nitrogen.
Nitrogen is needed in the nucleic acids of cells.
Nitrogen is lost at each step in a food chain as organic waste.
Carbon Cycle:
Carbon is an essential constituent of life, as all organic compounds have carbon in them. Carbon is lost at each step in a food
chain as carbon dioxide from respiration, and as organic waste. The carbon lost at each level is not available for use in further
trophic levels.