# AS Biology Unit 2 Revision Cards Ch7-10

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When studying variation, why only look at sample and not whole thing?
Too time consuming and impossible to catch each individual --> samples model whole population
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How can we prevent sampling bias? Give an example of a 3 step method.
Eliminate human involvement in choosing samples (random sampling) e.g. 1. divide area into grid of numbered lines 2. using random numbers obtain a series of co-ords 3. take samples at intersection of each pair of co-ords
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How can we minimise the effect of chance?
Use a large sample size, and analyse the data collected
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What are two causes of variation?
Genetic differences (set the limits) , and environmental influences (determine where within those limits an organism lies)
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Give 3 reasons for genetic differences
1) mutations- sudden changes to genes may be passed on to next gen. 2) meiosis- nuclear division forming gametes mixes up genetic material. 3) fusion of gametes- inherit different characteristics from each parent
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What do environmental influences effect?
The way a gene is expressed
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Give an example of DISCONTINUOUS traits. What are they caused by and what type of graph are they represented on?
e.g. blood type. Caused by genes. Represented on a bar chart.
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Give an example of CONTINUOUS traits. What are they controlled by? What type of graph are they represented on? What type of curve are they shown in?
e.g. hight/mass. Controlled by more than one gene (polygene). Represented in line graphs/histograms. Shown in NORMAL DISTRIBUTION CURVE. (bell-shaped curve)
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What is the mean? What are its pros and cons?
The max. height of a normal distribution curve. PRO= provides average value- useful for comparison. CON= doesn't provide info about the range
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What is the standard deviation?
Measure of width on normal distribution curve (from mean to point of inflection) It indicates the range of values either side of the mean- how spread out the numbers are.
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How do we calculate the standard deviation?
Find mean. Subtract it from each value. Square each answer. Add together. Divide by sample size. Square root.
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What is DNA made from, and what does that make it?
nucleotides... a polynucleotide!
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What is each nucleotide made from?
A phosphate group, a pentose sugar ( DEOXYRIBOSE) , a nitrogenous base with four possibilities (A, T, C, G)
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Which two out of those three remain the same?
Phosphate group and pentose sugar.
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How is the sugar-phosphate backbone formed?
Nucleotides join together to form polynucleotidic strands between phosphate group of one and pentose sugar of another
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How does the formation of the double helix occur?
Two polynucleotidic strands join by hydrogen bonds between bases via SPECIFIC BASE PAIRING. The two strands wind up to form the double helix.
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What is DNA's function?
Passing on genetic information from cell to cell and generation to generation
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How is DNA adapted to carry out its function? Give 4 reasons (last one didn't fit, found on next card.)
1) Double helix --> V.stable + can pass onto different generations without change. 2) Strands joined only by H bonds --> can separate for replication. 3) V.large molecule --> can carry lots of genetic info
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The 4th reason
Base pairs within backbone --> genetic info protected from corruption by outside chemical and physical forces
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Which base pairs with what and how many H bonds between them?
Adenine - Thymine ( 2 H BONDS) and Cytosine- guanine (3 H BONDS)
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What is a gene?
A section of DNA found on chromosomes which code for polypeptides
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Amino acids
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What is an amino acid coded for by?
3 bases in a gene- different sequences code for different amino acids
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What is the difference between DNA in a prokaryotic and a eukaryotic cell?
In a prokaryotic DNA form a circle and aren't associated with proteins. In Eukaryotic, DNA molecules are larger and form a line
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Why do chromosomes appear in homologous pairs?
In sexually reproducing organisms, each parent contributes a set of chromosomes to the offspring- hence one of each pair derived from mother, one from father.
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What is the diploid number?
The total number of chromosomes (2n)
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What is the haploid number?
The total number of chromosomes in a gamete. (n)
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What is a homologous pair?
Two chromosomes with the same gene sequence, ( same genes in same loci, but not always same alleles) Come together during meiosis 1
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What is an allele?
A form of a certain gene. Every gene can exist in >1 form.
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Why are the order of bases in each allele slightly different?
So that they can code for slightly different versions of the same characteristic.
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What is a locus?
The position of a gene on a chromosome. Alleles coding for the same characteristic will be found in the same locus on each chromosome in a homologous pair.
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What are chromosomes made up of?
Two sister chromatids attached by centromeres.
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Why is meiosis necessary?
They form haploid gametes. If a gamete had a full set of chromosomes, the cells they would produce would have double! Therefore it is necessary to maintain a constant no. of chromosomes in adult of the species.
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How many nuclear divisions does meiosis involve?
2
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What happens before meiosis?
Interphase- Dna unravels and replicates so there are 2 copies of each chromosome.
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What happens in meiosis (1) ?
Homologous chromosomes pair up (with the pairs lining up in a random order) and their chromatids wrap around eachother
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What happens in meiosis (2) ?
Pairs of sister chromatids that make up each chromosome are seperated. 4 HAPLOID DAUGHTER CELLS PRODUCED (genetically different from one another)
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How does meiosis produce genetic variation in offspring? ( 3 ways- final way on next card)
Independent separation of homologous chromosomes leads to them containing different combo's of maternal and paternal chromosomes. Recombination of homologous chromosomes by crossing over.
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3rd way
Haploid gametes, each with different genetic make-up fuse RANDOMLY at fertilisation
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Describe independent segregation
Each chromosome lines up alongside its homologous partner, arranging themselves in a random line. Combinations of daughter cells with one of the pair and with which one of the other pairs depends on how they're lined up in parent cell.
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Describe genetic recombination by crossing over
(chromosomes each lined up alongside homologous partner in M(1) .) THEN: chromatids of each pair twist round eachother, creating tension and so portions of chromatids break off. Broken portions then rejoin with chromatid of homologous partner.
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Why does this create genetic variation? (2 points)
4 different types of gamete produced as opposed to only 2. The crossover points- chiasmata- occur at random.
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Describe process of artificial selection
Individuals with desired characteristics identified and used to parent next generation. Offspring that don't display desired characteristic are prevented from breeding --> alleles for unwanted characteristics bred out of population
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How does artificial selection act as a genetic bottleneck?
Alleles in the gene pool are deliberately restricted to a small number of desired alleles. (hence leading to reduction in genetic diversity)
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What is the founder effect?
When a few organisms from a population start a new colony, leading to a change in the frequency of alleles.
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Why is there a higher incidence of genetic disease when founder effect occurs?
Only a small no. of organisms contribute their alleles to the gene pool --> INBREEDING
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What does the founder effect occur as a result of?
Migration leading to geographical separation / new volcanic islands forming
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Why could it lead to a new species?
There a fewer alleles and hence they are less able to adapt to changing conditions.
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What is a genetic bottleneck?
an event that causes a previously large population to be so reduced in numbers that only a few individuals survive
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Why is genetic diversity reduced?
Frequency of alleles in the gene pool of survivors is different from no. of alleles in larger population- there are less variety.
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Why are there differences within the gene pool?
Due to recombination of parental chromosomes in the zygote, crossing over and independent assortment during meiosis, and mutations
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What is non-coding DNA?
DNA inbetween genes which may or may not have an important function. (also contained within genes themselves as introns)
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What are the ethical implications of artificial selection?
Interfering with nature. What features selected for and who decides? How do we balance yield with animal welfare? Reduces genetic diversity and can cause genetic disease due to inbreeding.
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What does inbreeding promote?
Homozygosity (ZZ or zz) where zz means that a genetic disease is suffered from.
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What does outbreeding promote?
Heterozygosity (Zz)
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What is a haemoglobin molecule?
The oxygen-carrying pigment in red blood cells
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What type of protein and with which structure?
Globular, quaternary structure.
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How many haem groups does haemoglobin have and what do haem groups contain/do?
4. Each contains a ferrous ion (Fe2+) which can combine with a single oxygen molecule making a total of 4 O2 molecules carried by a single haemoglobin
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What is the role of haemoglobin?
To transport oxygen from lungs to the rest of the body
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How does it do this?
combines with O2 to form oxyhaemoglobin and releases O2 in tissues where the conc. is low.
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How is it adapted to be efficient?
It readily associates with oxygen at the gas exchange surface (where po2 is high) and readily dissociates with oxygen at tissues requiring it (where pO2 is low)
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How does it change its affinity for oxygen depending on the conditions?
Shape changes in different concentrations of CO2 due to change in pH. This change in shape causes it to bind more loosely to the oxygen and therefore it releases it.
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What colour is oxygenated blood?.... What about Deoxygenated blood?
Bright red..... Purple.
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What does a high affinity for O2 mean? - which organisms will this type of haemoglobin be found in?
Oxygen taken up easily, released less easily. - organisms living in an environment with low oxygen availability.
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So what adaptations will these organisms have to have?
Haemoglobin with high affinity to absorb enough, and a low metabolism so slow release of O2 is not a problem
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hat does a low affinity for O2 mean? -which organisms will this type of haemoglobin be found in?
Take up oxygen less easily, but release it more readily. In organisms with a high metabolic rate.
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So what adaptations will these organisms have to have?
Haemoglobin with low affinity so oxygen readily released into respiring tissues, and live in an environment with plentiful oxygen so low affinity isn't an issue
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Why are the two types of haemoglobin different? (DNA-wise)
Different sequences of amino acids, different number of polypeptide chains and number of haem groups and hence slightly diff. shapes!
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Where does oxygen loading take place? and where does oxygen dissociation take place?
Lungs. Respiring tissues.
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On an oxygen dissociation curve, further to the left/right has greater O2 affinity?
Further to the left has greater affinity.
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What is partial pressure?
A measure of a concentration of a gas proportional to its % by volume in a mixture of gases
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Why is the oxygen dissociation curve S-shaped?
When haemoglobin combines with the first O2 molecule, its shape alters to make it easier for other molecules to join. HOWEVER, as haemoglobin becomes saturated, it becomes harder for the O2 molecules to join (hence plateaus)
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What is the bohr effect?
haemoglobin gives up O2 more easily in higher pCO2. Hence in respiring cells, oxygen dissociation curve shifts down and right as rate of oxygen unloading increases (hence lower affinity)
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What is the form of energy storage in plants?
Starch
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What is the structure of starch and why is it suitable to its function?
unbranched helical chain in form of small grains. It is a mixture of 2 polysaccharides: -amylose (forms helix --> compact shape) and amylopectin (many protruding branches --> hydrolysed easily)
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Why is it good that starch is insoluble?
No osmotic effect (otherwise plant would swell up!)
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What is energy stored as in animals?
Glycogen
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Describe its structure and how it is related to its function
similar to amylopectin but even more branched!- hydrolysed rapidly- glucose released rapidly. Also compact --> good for storage
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What is cellulose a major component of?
Cell Walls
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What is it made up of?
Long, unbranched chains of B-glucose
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Why does it form rigid-chain like molecules?
The OH of one atom is above plane, and the OH of another atom is below plane. Hence to form B1-4 glycosidic bonds, one molecule must be flipped relative to its neighbouring molecule.
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What intermolecular force is in between chains?
Hydrogen bonds
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Long, thin cells that form a continuous layer to absorb sunlight.
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How are they adapted to their function?
Large vacuole pushes cytoplasm and chloroplasts to edge of cell.
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List 3 properties of a chloroplast.
surrounded by highly selective double membrane. Grana = where 1st stage of photosynthesis occurs, made up of 100's of disk-like thylakoids which contain chlorophyll. The stoma = where 2nd stage of photosynthesis occurs and is a fluid filled matrix
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How have chloroplasts adapted to their functions?
Their granal membrane has a large SA for attachment of chlorophyll and enzymes. Chloroplasts also contain DNA and ribosomes so can quickly and easily manufacture proteins needed for photosynthesis.
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What do cell walls consist of?
A number of polysaccharides- e.g. cellulose
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What are middle lamella?
They mark the boundary between adjacent cell walls and cement cells together
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What is the cell walls function? (3)
To provide mechanical strength to stop cell bursting (1) and to the plant as a whole (2). It also allows water to pass along it and hence contributes to movement of water throughout plant (3)
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List 4 differences between a plant and an animal cell
A plant has a cell wall (1) and lots of chloroplasts (2). It also has one large singular vacuole filled with cell sap (animals occasionally have small scattered ones). (3) Plants use starch grains for storage- animals use glycogen granules (4)
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What are the 2 main stages of cell division?
Nuclear division (process by which nucleus divides- mitosis/meiosis) and cell division (process by which whole cell divides)
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## Other cards in this set

### Card 2

#### Front

How can we prevent sampling bias? Give an example of a 3 step method.

#### Back

Eliminate human involvement in choosing samples (random sampling) e.g. 1. divide area into grid of numbered lines 2. using random numbers obtain a series of co-ords 3. take samples at intersection of each pair of co-ords

### Card 3

#### Front

How can we minimise the effect of chance?

### Card 4

#### Front

What are two causes of variation?

### Card 5

#### Front

Give 3 reasons for genetic differences