Download Biology Unit 2 AQA Additional Science

12/03/2014
AQA Additional Science
Biology Unit 2
B2.1 Cells and Cell Transport
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A Typical Animal Cell
1) Cytoplasm - this is
where the reactions
happen and these are
controlled by enzymes
2) Nucleus –
controls the
cell’s activities
3) Cell Membrane –
controls what
comes in and out
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4) Ribosomes – protein
synthesis happens
here
5) Mitochondria energy is released
here during
respiration
A Typical Plant Cell:
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Cell wall – made
of cellulose which
strengthens the cell
Cell membrane
– controls what
comes in and out
Large vacuole –
contains sap and
helps support the
cell
Chloroplasts (containing
chlorophyll) – this is needed
for photosynthesis
Nucleus – controls
what the cell does and
stores information
Cytoplasm –
Chemical reactions
happen here
Bacteria and Yeast
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Bacteria and yeast are two examples of single-celled
organisms:
Bacteria – containing
cytoplasm and a
membrane surrounded
by a cell wall. The genes
are NOT in a distinct
nucleus.
Yeast – contain the
usual cytoplasm,
nucleus and membrane
surrounded by a cell
wall.
More specialised animal cells
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I.D:
Red Blood Cell
Function:
Carries oxygen around the
body
Features:
No nucleus and large
surface area
Ciliated
epithelial cell
White blood cell
Nerve cell
(neurone)
Egg cell (ovum)
Diffusion
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Diffusion is when something travels from an area of high
concentration to an area of low concentration. For example,
consider the scent from a hamburger…
The “scent particles” from
this hamburger are in high
concentration here:
Eventually they will
“diffuse” out into this area
of low concentration:
Oxygen passes into cells by diffusion
Diffusion Summary
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Diffusion is when particles spread from an area of high
concentration to an area of ___ concentration. The particles
move along a “concentration _____” and this process takes no
_____ (it’s a “passive” process”). Diffusion can be accelerated
by increasing the _______ of the particles, which makes them
move _______.
Words – faster, low, gradient, temperature, energy
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B2.2 Tissues, Organs and Organs
Cell specialisation
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During the development of a multi-celled organism cells
differentiate to form specialised cells:
Ciliated
epithelial cell
White blood cell
Nerve cell
(neurone)
Egg cell (ovum)
Cells, tissues, organs and systems
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Basically, all living things are
made up of cells…
A group of CELLS makes up a
TISSUE
A group of TISSUES makes up
an ORGAN
A group of ORGANS makes up a
SYSTEM
A group of SYSTEMS make up an
ORGANISM
Another example
Here’s another example in humans:
Muscle cells
Muscle tissue
Organ
System
Organism
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An example organ: The Stomach
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Consider one of the body’s most important organs – the
stomach:
The stomach contains many
different types of tissue,
including:
1) Muscular tissue, to “churn
up” the contents
2) Glandular tissue, to
produce digestive juices
3) Epithelial tissue, to cover
the outside of the stomach
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An example system: The Digestive System
The whole point of digestion is to break down our food so that we can get
the bits we need from it. Basically, here’s how it works:
1) Glands such as the
salivary gland and the
pancreas produce digestive
juices
2) Digestion occurs in the
stomach and small intestine
3) Bile is produced by the
liver and helps break down
fats
4) Food is absorbed in the
small intestine
5) Water is absorbed in the
large intestine, leaving
behind the faeces
Examples of Plant Tissue
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1) Epidermal tissue, which
covers the plant
2) Mesophyll, where
photosynthesis occurs
3) Xylem and phloem, which
are used to transport
substances around the plant
B2.3 Photosynthesis
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Photosynthesis
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Basically, photosynthesis is the process through which a plant
makes its own food using carbon dioxide and water:
That’s a nice plant. I’m
going to put it in the sun and
give it lots of water and air…
CO2
H2O
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Photosynthesis – the 4 things you need
SUNLIGHT
Gives the plant energy
CHLOROPHYLL
WATER
Travels up
from the roots
CARBON DIOXIDE
Enters the leaf through small
holes on the underneath
The green
stuff
where the
chemical
reactions
happen
Photosynthesis equations
Carbon dioxide + _____
Sunlight
Chlorophyll
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glucose + _____
Sunlight
6CO2
+ 6H20
Chlorophyll
C6H12O6 + 6O2
The GLUCOSE produced by photosynthesis is used by the
plant for _______ (through ____________). It is stored
in the plant as ___________.
Words – respiration, starch, water, oxygen, energy
Limiting Photosynthesis
What factors could limit the rate of photosynthesis?
1. Temperature – the best temperature is
about 300C – anything above 400C will
slow photosynthesis right down
2. CO2 – if there is more carbon dioxide
photosynthesis will happen quicker
3. Light – if there is more light
photosynthesis happens faster
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Drawing graphs of these factors
1. Temperature
Photosynthesis is controlled by
enzymes – these are destroyed
at temperatures above 400C
2. Carbon dioxide
Photosynthesis increases at
first but is then limited by a
lack of increase in temp or light
3. Light
Photosynthesis increases at
first but is then limited by a
lack of increase in temp or CO2
Encouraging Photosynthesis
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Using knowledge of limiting factors, explain how plant growth
is encouraged in a greenhouse:
What is the glucose used for?
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1) Glucose (sugar) can be used to make long chains of insoluble starch…
Glucose
molecules
Starch
molecule
2) Glucose can be used to make cellulose for cell walls…
Glucose
molecules
Cellulose
3) Glucose can be combined with nitrates to make proteins (for growth)…
Glucose
molecules
Proteins
4) Glucose can be converted into lipids (fats or oils) to store in seeds…
Glucose
molecules
Lipid structure
2 common nutrients…
Nitrates:


Used to make proteins
Lack of it leads to stunted growth
Magnesium:


Used to make chlorophyll
Lack of it leads to yellow leaves
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B2.4 Organisms and their Environment
Factors affecting organisms
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Various factors can affect the development of organisms:
Availability of
carbon dioxide
and oxygen
Temperature
Factors affecting
organisms
Availability of
nutrients
Amount of
water
Amount of
light
Taking samples of an ecosystem
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Using different “sampling techniques” we can measure changes
in an ecosystem. The two main measurements are:
1) The physical conditions of a habitat (temperature etc)
2) The populations of different species in that habitat
Some common ways of measuring…
Help!
Measuring
temp, pH etc
Taking animal
samples
Taking samples
using quadrats
B2.5 Proteins
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Introduction to Enzymes
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Enzymes are biological catalysts. They help the reactions
that occur in our bodies by controlling the rate of reaction.
An enzyme is basically a protein molecule made
up of long chains of amino acids. These molecules
are then “folded” to create a certain shape.
Proteins are used in hormones, antibodies and
muscle tissue.
The enzyme’s shape helps another
molecule “fit” into it:
Enzyme
This shape can be destroyed by
high temperatures or the wrong
pH:
Substrate
Enzymes
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Enzymes work best in certain conditions:
Enzymes are
denatured
beyond 40OC
Enzyme
activity
400C
Temp
Could be
protease (found
in the stomach)
Could be amylase
(found in the
intestine)
pH
Enzymes are used in industry to bring about reactions at
normal temperatures and pressures that would otherwise be
expensive. However, most enzymes are denatured at high
temperatures and can be costly to produce.
pH
Enzymes in digestion
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Amylase (produced in the mouth,
pancreas and small intestine) breaks
_______ (a carbohydrate) down into
glucose:
Protease (produced in the stomach,
pancreas and small intestine) breaks
_______ down into amino acids:
Lipase (produced in the pancreas and
small intestine) breaks fats (_____)
down into fatty acids and glycerol:
Words – blood, lipids, proteins, digestion, starch, smaller
Bloodstream
Enzymes can be produced by the body to help _______. When they come
into contact and react with food they break it down into ______ pieces
which can then pass into the ______:
The digestive system
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The whole point of digestion is to break down our food so
that we can get the bits we need from it…
The main foods
affected are
CARBOHYDRATES –
these are broken down
into GLUCOSE.
Hydrochloric acid is
produced in the
stomach to kill bacteria.
Digestion also depends
on “enzymes”...
Bile and The Liver
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Bile is a chemical produced in the
liver and stored in the gall
bladder. It has 2 functions:
1) It neutralises stomach acid
and produces alkaline
conditions for enzymes to
work in
2) It emulsifies (“breaks down”
fats:
Fat
globules
Fat
droplets
Industrial uses of enzymes
1) Enzymes are used in washing powders
to help digest fats and proteins in food
stains. Biological washing powders will
only work on 400C or lower.
2) Enzymes are used in baby foods to
“pre-digest” the proteins.
3) Enzymes are used to convert starch
into sugar which can then be used in
food.
4) Conversion of glucose into fructose
using isomerase – glucose and fructose
are “isomers” (they have the same
chemical formula), but fructose is
sweeter.
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B2.6 Aerobic and Anaerobic Respiration
Respiration Introduction
I enjoy taking samples using quadrats. In
order to do this, I need energy. Where does
this energy come from?
Our energy comes from a process called
respiration, which basically involves turning
food and oxygen into energy and this
reaction is controlled by enzymes.
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(Aerobic) Respiration
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All living organisms have to move, _____, reproduce etc. Each
of these life processes needs ENERGY. ___________ is the
process our bodies use to produce this energy:
Glucose + oxygen
water + carbon dioxide + ENERGY
The glucose we need comes from ______ and the oxygen from
_________. Water and carbon dioxide are breathed out.
The MAIN product of this equation is _________.
Respiration happens in _________ in cells.
Words – breathing, energy, grow, respiration, food,
mitochondria
Uses for this energy
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Animals and plants have many uses for the energy they
generate from respiration:
1) To build up sugars in ______
2) To build up body _______
3) To maintain a constant body ___________ (warm-blooded
mammals only)
4) To build up sugars, ________ and other nutrients in plants
5) To build up amino acids and ________
Words – nitrates, tissue, proteins, respiration, plants
Heart
rate/min
225
The Effect of Exercise
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Breathing
rate/min
Rest
Exercise
100
Recovery
175
75
125
50
75
25
5 mins
10 mins
15 mins
20 mins
During exercise the following things happen: heart rate increases,
breathing increases and arteries supplying muscles dilate. These three
things all help muscles to get the oxygen and glucose they need.
Muscles and exercise
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When we exercise our muscles are supplied with more oxygen
and glucose, increasing the rate of respiration.
Muscles store glucose as glycogen
which can then be converted back
into glucose during exercise.
Anaerobic respiration
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Unlike aerobic respiration, anaerobic respiration is when
energy is provided WITHOUT needing _________:
Glucose
lactic acid + a bit of energy
This happens when the body can’t provide oxygen quick enough
for __________ respiration to take place.
Anaerobic respiration produces energy much _______ than
aerobic respiration but only produces 1/20th as much.
Lactic acid is also produced, and this can build up in muscles
causing ______ and an oxygen ______.
This “debt” then needs to be “repaid” by deep breathing to
________ the lactic acid.
Words – debt, oxygen, fatigue, oxidise, aerobic, quicker
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B2.7 Cell Division and Inheritance
Modern Genetics
Guten tag! My name is Gregor Mendel. I
am the father of modern genetics because
of the work I did on pea plants in 1865…
Mendel’s experiment:
Take two plants; one which is
pure-bred for tallness and one
pure-bred for shortness, and
cross them:
X
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Modern Genetics
All the plants produced
were tall.
Now cross two of these plants…
3 out of every 4 plants
were tall, leading Mendel
to hypothesise that “for
every characteristic
there must be two
determiners”
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Modern Genetics
Achtung! Unfortunately, nobody knew
about chromosomes or genes when I
published my findings so no one believed
me until after my death, when more
powerful microscopes were available.
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Cells, Genes and Chromosomes
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Chromosomes contain the
genetic information (genes)
and are normally found in
pairs in the nucleus (humans
have 23 pairs). They are
replicated every time a cell
divides by mitosis.
Mitosis:
1.
Mitosis vs. Meiosis
Used for growth and repair of
cells
2. Produces a “clone”
3. Cells with identical number of
chromosomes and genetic
information are produced
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Meiosis:
1.
Used to produce gametes for
sexual reproduction – occurs in
the testes and ovaries
2. Each daughter cell has half the
number of chromosomes of the
parent
During meiosis copies of
the genetic information
are made and then the
cell divides twice to
form four daughter
cells.
Sexual Reproduction
The human egg and
sperm cell
(“GAMETES”) contain
23 chromosomes each
and are created by
meiosis.
When fertilisation happens the
gametes fuse together to make a
single cell called a ZYGOTE. The
zygote has 46 chromosomes (23
pairs) and continues to grow through
mitosis, producing cells with the
same genes.
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Stem Cells
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A while ago we considered examples of specialised cells:
Ciliated
epithelial cell
White blood cell
Nerve cell
(neurone)
Egg cell (ovum)
A “stem cell” is a cell that hasn’t yet become specialised and
can be found in embryos or bone marrow. These cells can be
used to treat certain conditions but the use of these cells is
very controversial.
Stem cell research
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Stem cells are cells that have not yet specialised:
Embryo
Egg and
sperm
Cloned
embryos
These stem cells have
the potential to develop
into any kind of cell. In
grown adults they can
be taken from bone
marrow or they can
come from embryos
from unused IVF
treatments. They can be
used to treat conditions
such as paralysis.
The ethical issue:
Should these embryos be treated as humans?
Making decisions
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Some questions cannot be answered by science and need to be
considered on ethical grounds.
Factors that might influence a decision:
• Beliefs/religion
• What does “the right thing” mean?
• “Playing God”
• Risks – acceptable or unacceptable?
• Social and economic contexts
Boy or Girl?
X
Y
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X
“Allele”
Girl
XX
XY
Boy
Mother
Boy or Girl?
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Son
Father
Daughter
Gamete
Zygote
Key words
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•This allele determines the development of a
characteristic
•This is formed when an egg is fertilised by a sperm
Allele
•This allele will determine a characteristic only if
there are no dominant ones
Dominant
•This word refers to a pair of chromosomes being
made of two different alleles of a gene
Recessive
•An egg or a sperm are called this
Homozygous
•This word refers to a pair of chromosomes being
made of two of the same alleles of a gene
•An alternative form of a gene
Heterozygous
How genes work DNA
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Some facts:
- DNA has a “double ______” structure
- This contains instructions on what a cell does, how the organism should
work etc
- The instructions are in the form of a ______
- The code is made up from the four ____ that hold the strands together
- The bases represent the order in which _____ acids are assembled to
make specific ________
- Everyone (apart from identical ______) has different DNA and people
can be identified by “DNA finger printing”
Words – twins, helix, amino, code, bases, proteins
Eye colour
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In eye colour the brown eye allele is dominant, so we call it
B, and the blue eye is recessive, so we call it b:
BB
Bb
bb
Homozygous
brown-eyed
parent
Heterozygous
brown-eyed
parent
Blue-eyed parent
What would the offspring have?
Eye colour
Example 1: A homozygous
brown-eyed parent and a
blue-eyed parent:
X
BB
Parents:
Gametes:
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Example 2: 2 heterozygous
brown-eyed parents
bb
Bb
B
B
b
b
B
b
Bb
Bb
Bb
Bb
BB
Bb
X
Bb
B
b
bB
bb
(FOIL)
Offspring:
All offspring have brown eyes
25% chance of blue eyes
Eye colour
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Example 3: A heterozygous brown-eyed
father and a blue-eyed mother:
Bb
B
b
Bb
Bb
bb
b
b
bb
bb
Equal (50%)
chance of
being either
brown eyed or
blue eyed.
Another method
Example 3: A heterozygous brown-eyed
father and a blue-eyed mother:
B
b
b
Bb
bb
b
Bb
bb
Father
Mother
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Example questions
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1) In mice, white fur is dominant. What type of offspring
would you expect from a cross between a heterozygous
individual and one with grey fur? Explain your answer with a
genetic diagram.
2) A homozygous long-tailed cat is crossed with a homozygous
short-tailed cat and produces a litter of 9 long-tailed kittens.
Show the probable offspring which would be produced if two
of these kittens were mated and describe the characteristics
of the offspring (hint: work out the kitten’s genotype first).
Inherited diseases
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1) Cystic fibrosis – a disorder or cell membranes. It’s caused
by recessive alleles so both parents need to be “carriers”:
Ff
X
Ff
2) Polydactyly – a condition where a person has extra fingers
or toes. It’s caused by a dominant allele so can be passed on
by a parent who already has it:
Pp
X
pp
Embryos can be screened for alleles that cause
these diseases before birth.
Family Pedigree Charts
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Consider the following chart of the offspring and
grandchildren between two polydactyly carriers:
Key:
= male
= female
= P allele
= p allele
Q. Describe the genotype and the phenotype of each
of the grandchildren. Also, which member of this
family has got polydactyly?
B2.8 Speciation
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Fossils
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Fossils provide evidence of early life and could have been formed in many
ways. Four examples:
This fossil of a bat
was formed due to
hard parts of the
animal not decaying
This fossil was formed by
parts of its body being
replaced by minerals
This bee and orchid
pollen were preserved
in amber – the amber
lacked some of the
conditions needed for
decay to happen
Fossilised footprints
Fossil records
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Fossil records can provide a useful way of observing a species’
development:
The “Stenheim
skull”, found in
Germany in 1933
Oh
no…
The problem is, many early forms of life only had soft bodies
and the few remaining traces of them have been destroyed by
geological activity. This makes it difficult for scientists to
know what happened in the distant past.
Extinct Species
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Sabre-toothed tigers
and mammoths
Dodo
Extinction
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Extinction can happen due to an organism’s
inability to adapt and die because of:
•
•
•
•
Increased _______
New predators
Changes in the _________
New diseases
Oh no…
Alternatively, a “mass extinction event” can
happen, for example the extinction of the
__________.
In modern days animals are in danger due to
_____ activity, e.g. pollution, hunting,
__________ etc…
Words to use: deforestation, competition, dinosaurs,
human, environment
Geographic isolation
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Different species can be formed by “geographic isolation”, for
example, consider an African elephant:
1) Elephants are separated by a
geographic feature e.g. a _________
2) Elephants on each side of the
mountain have different ______ in
their _____ pool
3) Some offspring have characteristics
that help them survive
4) Their weaker _______ die out and
the offspring are so genetically
removed that they’re incapable of
________ with each other – they’re
now different ________
Words – species, mutations, mountain, gene, ancestors, reproducing