Download Additional Biology – Summary notes

Additional Biology – Revision notes
A. Cells. Cells are the basic units of living things
Animal and Plant cells
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All cells contain a nucleus, cytoplasm and cell membrane
Plant cells contain a cell wall, permanent vacuole and chloroplasts
Cells that have a specific function have special adaptations
How do substances get in and out of cells?
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Particles in liquids and gases move randomly
Liquids and gases move in and out of cells randomly by diffusion
Diffusion is a process whereby substances move from an area of
high concentration into an area of lower concentration, which
causes mixing
Diffusion is a passive process
Osmosis
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Osmosis is the passage of water from an area of high
concentration into an area of lower concentration across a semi
permeable membrane
Osmosis is important in plants maintaining the shape and integrity
of cells.
Dissolved substances can move into and out of cells by
diffusion.
Water can move by Osmosis
www.cellsalive.com
B.How plants produce food
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During photosynthesis light energy is absorbed by a green
substance called chlorophyll, which is found in chloroplasts of plant
cells
The light energy is used to convert carbon dioxide and water into
sugar (glucose) and oxygen is released as a by-product
Limiting factors
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The rate of photosynthesis is determined by the supply of carbon
dioxide, temperature and availability of light
These factors interact, but if one of these factors is in short
supply the rate of photosynthesis is limited
How plants use glucose
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The glucose produced in photosynthesis may be converted into
insoluble starch for storage
Plant cells use some of the glucose produced in respiration
Why do plants need minerals?
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Plants absorb mineral salts for healthy growth
Nitrate is used to produce protein, plants lacking nitrate are
stunted
Magnesium is used to produce chlorophyll; plants lacking magnesium
have yellow leaves
Pyramids of biomass
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The ultimate source of all energy for living things is the sun
The mass of living material at each stage of a food chain is less
than the previous stage
The amount of biomass at each stage can be drawn to scale and
shown in a pyramid of biomass
Energy losses
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The amount of biomass and energy contained in organisms is
reduced at each stage of a food chain because
During respiration heat is lost to the surroundings
Respiration supplies the energy for all life processes including
movement
Some materials and energy are lost as waste materials
Maintenance of a constant body temperature (mammals & birds)
which is usually higher than their surroundings means high energy
losses
Energy in food production
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At each stage in a food chain, less material and less energy are
contained in the biomass of the organisms
This means that the efficiency of food production can be improved
by
(i) reducing the number of stages in a food chain
(ii) restricting energy loss by food animals by limiting their
movement
(iii) by controlling the temperature of their surroundings
Decay
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Living things remove the materials that they need for life
processes from their environment
These materials are returned to the environment either in waste
materials or when they die & decay
Materials decay because they are digested by micro-organisms.
Warm moist conditions with plenty of oxygen are the best
conditions for microbe activity
The Carbon cycle
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The constant recycling of carbon is called the carbon cycle.
Plants remove carbon dioxide from the atmosphere during
photosynthesis
Respiration, death & decay returns carbon dioxide to the
atmosphere
Organic /intensive farming
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There are advantages and disadvantages of organic and nonorganic farming techniques
Compromises need to be struck to ensure production of enough
high quality foodstuffs
There is a compromise between efficient food production and the
practical mechanisms of animal husbandry/ making it work
www.soilassociation.org and www.rhs.org.uk
C. Enzymes
Enzyme structure
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Catalysts alter the rate of chemical reactions
Enzymes are proteins
Enzymes are catalysts produced by cells
Enzymes have a special shape which allows other chemicals to fit
into them
Factors affecting enzyme action
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Enzymes are proteins their shape is important to their functioning.
Changes in pH, high temperatures alter protein shape
Enzymes in digestion
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Digestive enzymes are produced by specialised cells in glands & in the
lining of the gut
The enzymes pass out of the cells and into the gut; they catalyse the
breakdown of large molecules into smaller ones
Amylase is produced in the salivary glands and pancreas and catalyses the
breakdown of starch into sugar
Protease is produced by the stomach and pancreas it catalyses the
breakdown of proteins into amino acids
Lipase is produced by pancreas & small intestine and catalyses the
breakdown of fats into fatty acids and glycerol
Speeding up digestion
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Protease enzymes are produced by the stomach, the stomach
produces Hydrochloric acid. The enzymes in the stomach work most
effectively in these conditions
The liver produces bile. The bile is stored in the gall bladder. Bile
neutralises the acid that was produced in the stomach.
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The enzymes of the small intestine work best in alkaline conditions.
Bile emulsifies fats ( breaks them into small droplets)
Aerobic respiration
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Aerobic respiration occurs in the mitochondria of cells
It is controlled by enzymes and is the slow controlled release of
energy from the reaction of glucose with oxygen
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Glucose + Oxygen
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The energy from respiration is used for life processes
Carbon Dioxide + Water
Making use of enzymes
Some micro-organisms produce enzymes that pass out of the cells.
These microbes can be cultured to obtain the enzymes. These
enzymes have many uses including
(i)
Biological detergents – protein and fat digesting enzymes
(ii)
Food industry - baby foods (proteins “pre-digested”).
(iii)
Isomerase converts glucose into fructose syrup which is
much sweeter and used in smaller quantities in slimming
foods- Carbohydrases convert starch into sugar syrup.
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D. Controlling internal conditions
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The internal conditions of the body which are controlled
include water content of body, ion content, and temperature
and sugar levels
Waste products need to be removed; these include carbon
dioxide from respiration, urea from the break down of amino
acids
The monitoring and control of the body’s internal
environment is called homeostasis
Controlling body temperature
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The Body temperature is monitored and controlled by
thermoregulatory centre in the brain
All cellular reactions are controlled by enzymes
Changes in temperature affect the rate at which enzyme
controlled reactions occur
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If the core body temperature falls, blood vessels supplying the
skin capillaries constrict, to reduce heat loss. Muscles may “shiver”
to generate heat
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If the core body temperature rises, blood vessels supplying the
skin capillaries dilate, causing increased blood flow and heat is lost.
Sweat glands release sweat which cools the body as it evaporates
Controlling blood sugar
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Blood glucose levels are monitored and controlled by the pancreas
The pancreas produces 2 hormones, Insulin and glucagon
Insulin allows blood to be taken up by liver and muscle cells to be
stored as an Glycogen, which is an insoluble carbohydrate
Glucagon converts the glycogen back into glucose
Diabetes is a disease in which a person cannot control there
blood glucose levels
www.diabetes.org.uk
E. Cell division and growth (Mitosis)
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In body cells the chromosomes are found in pairs. (homologous
pairs)
Body cells divide by mitosis to produce additional cells during
growth, repair or replacement
Most animal cells differentiate (specialise) at an early stage.
Stem cells
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Cells from human embryo’s and adult bone marrow, called stem
cells, can be made to differentiate into many different types of
cells
Treatment with these cells can be used to help conditions such as
leukaemia
www.christopherreeve.org
Cell division in sexual reproduction (Meiosis)
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www.stemcellresearchfoundation.org
Body cells contain two sets of chromosomes (Diploid)
Gametes contain one set ( Haploid)
Cell division to produce gametes is called Meiosis ( reductive
division)
simplified outline of the process
Copies of chromosomes made
Cell divides twice to form 4 gametes
When gametes join at fertilisation, the new cell has 2 sets of
chromosomes, with information from each parent this gives rise to
variation
From Mendel to DNA
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Chromosomes are made up of large molecules of DNA (deoxyribose
nucleic acid).
The DNA molecule looks like a spiral stair case (called a double
helix)
The rungs are made of base pairs
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There are 4 bases. Adenine (A) pairs with Thymine (T), Cytosine
(C) pairs with Guanine (G)
The combination of the bases codes for particular amino acids
which make up proteins
Each chromosome consists of Genes
Some characteristics are controlled by a single gene
Each gene may have different forms called Alleles
Some alleles are dominant (Capitol letter L ) others are recessive
(lower case l)
www.mendelweb.org
Inheritance in action (simple genetics)
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Humans have 23 sets of chromosomes
The 23rd set determines gender
In females the chromosomes are the same (XX)
males the chromosomes are different (XY)
www.newbyte.co.uk
Inherited conditions in humans
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Some diseases are inherited
Cystic fibrosis is inherited through a recessive allele
Huntington’s is inherited through a dominant allele
Genetic counselling allows a couple to work out the probability of a
child inheriting a disease
Embryo screening will determine if an unborn child has inherited a
disease
Stem cells and embryo’s – an ethical minefield
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What do we mean by something being ethical?
When we say something is a minefield, what do we mean?
There are many opposing views on use of stem cells and embryo’s in
research
Guidelines and rules for use of human cells are strictly controlled
There are many valid reasons for use and very strongly held views against
the use of human materials in research
www.hdfoundation.org
www.cftrust.org
www.cff.org
www.welcome.ac.uk