Download Biology B2 Revision Notes

B2: The Components of Life Revision Notes
Topic 1 - The building blocks of cells
1.1 Bacterial cells
- chromosomal DNA (contains most genetic material)
- plasmid DNA (small loops, carries extra info e.g. antibiotic
resistance genes)
- flagella (long, whip-like structures to help them move)
- cell wall (flexible, not made of cellulose, supports cell)
1.2 Plant cells
- chloroplast (contain chlorophyll for photosynthesis)
- large vacuole (filled with sap, helps keep cell rigid)
- cell wall (supports cell and keeps its shape)
- cell membrane (controls what substances go in and out of the cell)
- mitochondria (respiration happens here, found in cytoplasm)
- cytoplasm (many chemical reactions happen)
- nucleus (contains DNA, controls cell)
1.3 Animal cells
- cell membrane
- mitochondria
- cytoplasm
- nucleus
(see 1.2 for functions)
1.4 Plant and animal cells can be studied in greater detail with a light
microscope – light passes through specimen and lenses make you see it
bigger
1.5 Changes in microscope technology have enabled us to see cells with more
clarity and detail than in the past – light telescope = x1500, electron
microscope = x2million. Electron microscope sees far greater detail and has
helped identify smaller structures in the cell e.g. DNA
1.6 A gene is a section of a molecule of DNA and that it codes for a specific protein
1.7 DNA molecule have:
a two strands coiled to form a double helix
b strands linked by a series of complementary base
pairs joined together by weak hydrogen bonds:
i adenine (A) with thymine (T)
ii cytosine (C) with guanine (G)
1.8 Investigate how to extract DNA from cells
Method:
1. Crush fruit/vegetable to separate cells.
2. Add salt and washing up liquid to break down cell membranes.
3. Filter.
4. Add protease to release the DNA from the proteins.
5. Slowly pour ice cold ethanol down the side of the test tube.
6. The DNA is found in the layer between the ethanol and the fruit/vegetable solution layer.
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1.9 Explain an understanding of how the structure of DNA was discovered
Franklin and Wilkins – looked at DNA structure using x-rays
Watson and Crick – used data, including x-rays by Franklin, to build double helix model
1.10 (H) Sequencing the human genome (Human Genome Project) was collaboration – 18 countries, 13 years
Implications – improved testing for genetic disorders, finding genes that may increase the risk of certain
diseases, new treatments and cures, looking at changes in the genome over time, personalized medicines.
1.11 Genetic engineering - the removal of a gene from the DNA of one
organism and the insertion of that gene into the DNA of another organism
1.12 GM organisms:
a beta carotene in golden rice to reduce vitamin A deficiency in humans
adv – reduces blindness in developing countries
disadv – GM rice may breed with wild rice and contaminate its DNA, some people think it is not
safe to eat, expensive to buy and does not produce fertile seeds
b producing human insulin by genetically modified bacteria
adv – do not have to extract from dead animals, vast quantities can be produced, made more
cheaply
disadv – insulin produced is slightly different to human insulin
c producing herbicide-resistant crop plants
adv – herbicide doesn’t kill crops
disadv – development of herbicide resistant weeds, loss of biodiversity as all other plants are killed,
loss of food/shelter for animals
1.13 Mitosis produces two daughter cells, each with identical
sets of chromosomes in the nucleus to the parent cell,
resulting in the formation of two genetically identical diploid
body cells
1.14 Mitosis occurs during growth, repair and asexual
reproduction
1.15 At fertilisation, haploid gametes combine to form a diploid zygote
1.16 Meiosis produces four daughter cells, each with
half the number of chromosomes, this results in the
formation of genetically different haploid gametes
1.17 Cloning is an example of asexual reproduction that
produces genetically identical copies
1.18 (H) The stages in the production of cloned mammals:
a removal of diploid nucleus from a body cell
b enucleation of egg cell
c insertion of diploid nucleus into enucleated egg cell
d stimulation of the diploid nucleus to divide by mitosis
e implantation into surrogate mammals
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1.19 Cloning mammals:
Advs – making genetically identical copies of an adult organism that has desirable characteristics e.g. bulls
that produce high quality calves; making copies of animals that have been genetically modified e.g. cows
that produce insulin in milk
Disadvs – difficult; low success rate for cloned embryos; health problems in cloned mammals; if one
animal is susceptible to a disease, all the clones will be too
1.20 Stem cells in the embryo can differentiate into all other types of cells, cells lose this ability as the
animal matures – the differentiation of adult stem cells is limited
1.21 Stem cell research:
Adult Stem Cells
Advs – can use the patients own cells; partially differentiated so easier to make them into the correct type
of cell
Disadvs – difficult; not possible for some cell types
Embryonic stem cells
Advs – can produce a wide range of cells; use unwanted embryos from IVF treatment; easier to grow
Disadvs – destroys the embryo – killing life?
1.22 The order of bases in a section of DNA decides the order of amino acids in the protein – 3 bases from
DNA code for 1 amino acid. Amino acids are joined together to form a protein
1.23 Protein synthesis:
a the production of complementary mRNA strand in the nucleus
transcription
b the attachment of the mRNA to the ribosome
c the coding by triplets of bases (codons) in the mRNA for specific amino acids
d the transfer of amino acids to the ribosome by tRNA
e the linking of amino acids to form polypeptides
Transcription
Translation
translation
1.24 Each protein has its own specific number and sequence of amino acids, resulting in different-shaped
molecules that have different functions, including enzymes
1.25 Gene mutations change the DNA base sequence, e.g. AGGCGTA to AGGTGTA
Harmful – if the mutation changes the shape of a protein, e.g. sickle cell
Beneficial – e.g. bacterial resistance
Neither – most mutations do not change the order of amino acids in a protein so do not affect the protein
shape
1.26 Enzymes are biological catalysts
1.27 Enzymes catalyse chemical reactions:
a DNA replication (inside cells) – separates DNA strands, joins the bases of the new strand
together
b protein synthesis (inside cells) – e.g. join amino acids together
c digestion (outside cells) – break down food into molecules small enough to pass across
membranes
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1.28 Factors affecting enzyme action:
a temperature – human enzymes work best at 370, temp too low = slow reaction, temp too high =
enzyme denatured (loses shape and substrate no longer fits)
b substrate concentration – more substrate = faster reaction until a point when the enzyme is
working as fast as it can
c pH – most work best at pH7 (in stomach pH1-2, small intestine pH8), pH too low or too high =
enzyme denatured
Temperature
Substrate Concentration
pH
1.29 Enzymes are highly specific for their substrate – each enzyme only fits one substrate
1.30 The ‘lock-and-key’ hypothesis – only one key can open a lock, only one type of enzyme can speed up a specific
reaction
1.31 Enzymes can be denatured (lose their shape) due to changes in the shape of the active site
1.32 Investigate the factors that affect enzyme activity
The effect of temperature method:
Amylase breaks starch down into glucose.
1. Measure 5ml starch solution and 1ml amylase into separate test tubes and place in
water bath at 20oC for 3 mins. (allows both solutions time to reach the correct
temperature)
2. Set out a spotting tile with a drop of iodine in each well. (Iodine black = starch
present, Iodine stays brown/orange = no starch present)
3. Add the amylase to the starch solution and immediately take your 0 min sample with a
dropper.
4. Test a drop of the sample every minute for 10 minutes. Wash out pipette between
uses. (prevents contamination of next sample)
5. Repeat again at 40oC and 60oC.
At 20oC it takes longer as the enzymes are catalyzing the reaction more slowly. At 40 oC it is quickest as
this is nearest human body temperature (37oC). At 60oC it does not catalyse at all as the enzyme has
been denatured.
The effect of pH method:
Pepsin is found in the stomach (pH2).
1. Measure 5ml albumin into test tube. Add 3 drops of acid. Add 1ml pepsin.
2. Put in water bath for 30 mins.
3. If still cloudy = albumin not broken down by pepsin, if clear = albumin broken down
4. Repeat with 3 drops of water/alkali instead of acid.
In alkali and neutral (water) the pepsin does not break the albumin down – pepsin is denatured. In acid
the albumin is broken down so turns clear – optimum pH.
The effect of substrate concentration method:
See 3.17 using visking tubing, starch solution and amylase.
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Topic 2 - Organisms and energy
2.1 Respiration is a process used by all living organisms that releases the energy needed for life processes
2.2 Circulatory system facilitates respiration by:
a glucose and oxygen diffusing from capillaries into respiring
b carbon dioxide diffusing from respiring cells into capillaries
cells
2.3 Diffusion is the movement of particles from an area of high concentration to an area of lower
concentration
2.4 Aerobic respiration uses oxygen to release energy from glucose
2.5 Investigate the effect of exercise on breathing rate and heart rate
Method:
1. Take resting heart rate and breathing rate. (Time how many beats/breaths in 15 seconds and
multiply by 4 to get the number per minute.)
2. Walk for 2 mins, retake heart and breathing rates. Retake both rates every minute until back to
resting rates.
3. Repeat with jogging and/or running.
2.6 Heart rate and breathing rate increase with exercise – increased exercise = more energy from
respiration = more O2 and glucose needed = increased breathing rate to get more oxygen, increased
heart rate to distribute O2 and glucose to cells
2.7 Cardiac output = stroke volume x heart rate
2.8 During vigorous exercise muscle cells may not receive sufficient oxygen for their energy requirements
and so start to respire anaerobically
2.9 Anaerobic respiration releases energy from glucose
2.10 Anaerobic respiration releases less energy than aerobic respiration
2.11 The build-up of lactic acid requires extra oxygen to break it down. This is called excess post-exercise
oxygen consumption or EPOC (formerly known as oxygen debt)
lactic acid + oxygen -> CO2 + H2O
2.12 Heart rate and breathing rate remain high after exercise - O2 still needed = breathing rate high to
get oxygen, heart rate high to distribute O2 to cells
2.13 The structure of a leaf is adapted for photosynthesis:
a large surface area – absorbs as much light as possible
b containing chlorophyll (green pigment) in chloroplasts to absorb light
c stomata (pores in leaf) for gas exchange (carbon dioxide, oxygen and water vapour)
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2.14 Photosynthesis uses light energy to produce glucose
carbon dioxide + water -> glucose + oxygen
2.15 Limiting factors that affect the rate of photosynthesis:
a light intensity – dim light = slow photosynthesis
b CO2 concentration – low CO2 = slow photosynthesis
c temperature – low temp = slow photosynthesis, high temp = slow photosynthesis
2.16 Investigate how factors, including the effect of light intensity, CO 2 concentration or temperature, affect the rate of
photosynthesis
Method for light intensity:
1. Set up a lamp and a beaker with some pond
weed under water. Place an upturned funnel
over the pondweed.
2. Put the lamp 10cm away from the pond
weed. Count how many bubbles were
produced in 1 minute.
3. Repeat at distances of 20cm, 30cm, 40cm
and 50cm.
Method for temperature:
1. Set up as detailed above. Keep the distance of the light constant but use different temperatures.
Method for CO2 concentration:
1. Set up as detailed above.
2. To get different CO2 concentrations use different amounts of sodium hydrogen carbonate which
adds CO2 to the water.
2.17 The loss of water vapour from leaves drives transpiration
2.18 Transportation through a plant:
a mineral uptake in roots by
transport (movement of
molecules against the
concentration gradient –
from low concentration to
high concentration. Requires
energy.)
b xylem (transports water active
mineral salts)
phloem (transports glucose)
2.19 Root hair cells are adapted to take up water by osmosis:
They have:
1. Large surface area for substances to enter the root
2. Thin cell walls so substances can easily cross into the cell
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2.20 Osmosis is the movement of water molecules from an area of higher concentration of water to an
area of lower concentration of water through a partially permeable membrane
2.21 Investigate osmosis
Method:
Potato cells have a semi-permeable membrane and water can pass across it by osmosis.
1. Use cork borers to make potato cylinders and cut to 2cm in length. Weigh potato.
2. Use sucrose solutions 0%, 20%, 40%, 60%, 80%, 100%.
3. Put potato into 20ml sucrose solution and leave for at least 30mins.
4. Dry potato, measure length and weight.
Potato in high concentration sucrose solutions will lose length/mass as the concentration of water
molecules is higher in the potato so they will move out into the sucrose solution. Potato in low
concentration sucrose solutions will gain length/mass as the concentration of water molecules is higher in
the sucrose solution so they will move into the potato.
2.22 Investigate the relationship between organisms and their environment using fieldwork techniques
Method:
1. Choose 2 different areas.
2. Use random number generator to generate coordinates for around 10% of the area.
3. Use quadrat at these coordinates – count number of species as well as counting the number of
specific plants, e.g. daisies.
4. Calculate averages for number of species and numbers of specific plants for each area.
2.23 Investigate the distribution of organisms in an ecosystem, using sampling techniques including:
a pooters- used to catch small insects
b sweep nets/pond nets – used to catch flying insects / pond invertebrates
c pitfall traps – used to catch invertebrates
d quadrats – used to sample plants
Pooter
Sweep Net
and measure environmental factors including:
e temperature – use thermometer
f light intensity – use light intensity meter
g pH – use pH probe
Pitfall Trap
Quadrat
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Topic 3 -
Common systems
3.1 Fossil record provides evidence for evolution – history of life on Earth through thousands/millions of
years
3.2 There are gaps in the fossil record because:
a fossils do not always form
b soft tissue decays
c many fossils are yet to be found
3.3 The anatomy of the pentadactyl (5 fingered) limb provides
scientists with evidence for evolution



Most vertebrates (and vertebrate fossils) have similar
limb bone structure.
Suggests a common ancestor millions of years ago.
Adapted over millions of years to allow different ways to
move.
3.4 Growth can be described as increase in size, length and/or mass
3.5 Percentile charts – e.g. 20th percentile = 20% of the
data are equal to or below that line
Used to check that children are growing normally (normal =
between 5th and 95th percentile)
3.6 Cell division, elongation and differentiation contribute to the
growth and development of a plant
3.7 Cell division and differentiation contribute to the growth and
development of an animal
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3.8 Parts of the blood:
Red blood cells
 Contain red pigment = haemoglobin
 Biconcave in shape – large surface area for O2 to
diffuse in and out
 No nucleus – more room for haemoglobin
White




blood cells
Have nucleus
Defend against disease
Some produce antibodies that bind to microbes
Some surround and destroy foreign cells that get
into the body
Plasma
 Yellow liquid
 Transports dissolved substances e.g. CO2, hormones
Platelets
 Tiny fragments of cells (no nucleus)
 Important for blood clotting and forming scabs
3.9 Cells are grouped into tissues (a group of the same specialized cells), tissues into organs (several
tissues working together to do a certain job), and organs into organ systems
3.10 The heart is:
a there are four major blood vessels associated with the heart
 pulmonary artery (takes blood to lungs)
 pulmonary vein (brings blood back from lungs)
 aorta (takes blood to the rest of the body)
 vena cava (brings back blood from the rest of the body)
b left atrium and ventricle to pump oxygenated blood from lungs to the rest of the body
c right atrium and ventricle to pump deoxygenated blood to the lungs
d valves to prevent backflow in heart
e left ventricle has a thicker muscle wall than the right ventricle (has to pump all the way round
the body rather than to just the lungs)
f the direction of blood flow through the heart – right atrium -> right ventricle -> lungs -> left
atrium -> left ventricle -> rest of body (back to right atrium again)
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3.11 The circulatory system transports substances around the body, including:
a arteries transport blood away from the heart
b veins transport blood to the heart
c capillaries exchange materials with
tissues
3.12 The digestive system:
1. Mouth
 Teeth break up food increasing surface area
 Saliva lubricates food and contains amylase (an enzyme)
2. Oesophagus
 Muscular tube
 Moves food by peristalsis
3. Stomach
 Muscular bag that makes acid and some enzymes
 Churns up food by peristalsis
4. Small intestines
 Most large molecules are broken into smaller molecules
 Contains lots of enzymes made by itself and the pancreas
 Small molecules of food are absorbed into blood using villi
 Food is moved by peristalsis
5. Pancreas
 Makes enzymes which are released into the small intestines
6. Large intestines
 Thin-walled tube
 Water diffuses from undigested food through wall
7. Anus
8. Liver
 Food dissolved in plasma gets processed here
 Some molecules are broken down further and others are built
up
 Bile is made here which helps to digest fats
9. Gall bladder
- Stores bile and releases it into the small intestine
3.13
The alimentary canal (a muscular tube running from mouth to anus)
Peristalsis (waves of muscular contractions that move food along the alimentary canal)
3.14 Digestive enzymes:
a Carbohydrases which digest starch to simple sugars
e.g. amylase found in saliva and also it is released into the small intestine from pancreas
b Proteases which digest proteins to amino acids
e.g. pepsin – made in stomach, optimum pH is 2
c Lipase digests fats to fatty acids and glycerol
3.15 Bile is alkaline so neutralises stomach acid and makes small intestine pH8.
It emulsifies fats – breaks down large globules into tiny droplets forming an
emulsion. The smaller droplets have a larger surface area for lipase to act on.
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3.16 Villi (finger-like folds in the lining of the small intestine) have large
surface area, single layer of cells and capillary network to allow efficient
absorption of the soluble products of digestion. The network of capillaries
ensures there is always a low concentration of soluble food molecules in
the blood so there is a steep concentration gradient = rapid diffusion.
3.17 Investigate the effect of different concentrations of digestive enzymes, using and evaluating models of the
alimentary canal
Method:
The visking tubing is representing the wall of the gut. The starch is in long chains so cannot pass through
the visking tubing. It is broken down by the amylase into sugars. Sugars are small enough to pass
through the visking tubing. Sugar can be tested for using Benedicts solution.
1. Add 20ml of starch solution to the visking tubing
which has been tied at one end. Add 1ml amylase. Tie
the other end of the tubing.
2. Rinse visking tubing and place in a beaker of water.
3. Take a sample of the water in the beaker every 5
mins and test for sugar using Benedicts solution. Blue
= no sugar, orange/red = sugar present.
4. Test with different concentrations of amylase solutions
(or use the same method with different starch
solutions for 1.32 – effect of different substrate
concentrations).
3.18 Claimed benefits of the use of functional foods as part of a healthy diet:
a probiotics containing Bifidobacteria and lactic acid bacteria Lactobacillus – live “friendly” bacteria which
are claimed to aid digestion, protect against disease and reduce allergies – not enough evidence
b prebiotic oligosaccharides – substances the body cannot digest and act as food for the “friendly”
bacteria which encourages their growth. Found in tomatoes, bananas, onions. Growing evidence
that they can increase beneficial bacteria in your gut so help maintain good health
c plant stanol esters – oily substances found in plants. Can stop the small intestine absorbing
cholesterol (which can cause heart disease). Used in many foods e.g. yoghurt – clear evidence they
have an effect
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