AS Biology Unit 2 Model Answers Flashcards
(112 cards)
1
Q
Gas exchange in plants
A
During respiration oxygen diffuses into the plant when the stomata are open
Carbon dioxide diffuses out of the plant
During photosynthesis carbon dioxide diffuses into the plant and oxygen diffuses out
In the mesophyll layer the plant has numerous interconnecting air spaces to aid gaseous diffusion
Gases do not have to be dissolved in water for diffusion through the stomata
Stomata can close to conserve water
When this happens no gas exchange can occur through the stomata
2
Q
What are the features of specialised exchange surfaces?
A
Large surface area to volume ratio
Thin so shorter diffusion pathway
Partially permeable
Movement of environmental medium to maintain a concentration gradient
Movement of internal medium to maintain a concentration gradient
3
Q
How have large organisms evolved to be efficient at diffusion?
A
A flattened shape
So that no cell is ever far from the surface
Specialised exchange surfaces with large areas
To increase the surface area to volume ratio
E.g. Lung or gills
4
Q
Gas exchange in insects
A
Air enters through the spiracles
And passes along the tracheae
There is a diffusion gradient in the tracheolus
Causing oxygen to diffuse into cells
Ventilation ( movement of muscles ) replaces air in the tracheae maintaining a concentration gradient
Spiracles are able to close
5
Q
How do respiratory gases move in and out of the tracheal system?
A
Down a concentration gradient (air moving in has high oxygen content, at the tissues the oxygen content is low as cells are using up oxygen in respiration)
Ventilation by the movement of muscles in the abdomen creates mass air movement
6
Q
Why fish gils are efficient at diffusion of oxygen
A
Numerous gill filaments with numerous lamallae
To increase surface area
Thin / squamous epithelium cells of gill and capillaries
So short diffusion pathway
Gills are well supplied with numerous small capillaries
This also increases the surface area
Steep concentration gradient maintained by countercurrent flow
Oxygen diffuses into blood along the whole length of the gill
Constant circulation of blood always takes blood high in oxygen away
Constant ventilation always increases oxygen content at gas exchange surfaces
7
Q
What else happens when spiracles close?
A
Conserve water
8
Q
What causes the spiracles to open?
A
The build up of carbon dioxide
9
Q
Due to insects not having a blood system what happens to the oxygen?
A
The oxygen diffuses straight into the tissues from the tracheolus
10
Q
What is the relationship between an organisms size and its surface are to volume ratio?
A
The bigger the organism, the smaller the ratio therefore the slower the rate of diffusion across the exchange surface
11
Q
How insects are adapted to conserve water?
A
Small surface area to volume ratio
Waterproof coverings on body surfaces
Ability to close spiracles
12
Q
How insects are adapted to increase gas exchange
A
Numerous spiracles to increase surface area
Short diffusion pathway as air in tracheoles connects direct to tissues (no blood)
Many numerous tracheoles to increase surface area
Concentration gradient maintained by ventilation and the removal of oxygen by respiring tissues
13
Q
Gas exchange in fish
A
Water enters through the mouth
And is forced across the gill filaments
The water flows on an opposite direction to the blood in the gill lamallae- this is countercurrent flow
This produces a concentration gradient
To promote the diffusion if oxygen from the water into the blood along the whole length of the gill
Water passes out through the operculum
14
Q
How plants are adapted to increase gas exchange
A
Numerous stomata increase surface area
Diffusion takes place in gas phase
No living cell is far from external air ( long, thin, flat shape of leaves)
Air spaces in spongy mesophyll
Sort diffusion pathway
Concentration gradient maintained by photosynthesis and respiration
15
Q
Structure of haemoglobin
A
Primary structure consists of 4 polypeptide chains built up of amino acids
Secondary structure consists of these chains coiled into the alpha helix connected with hydrogen bonds
Tertiary structure provides the 4 chains with specific globular shapes with further bonding
Quaternary structure - 4 chains are linked together to form a spherical molecule
Each polypeptide is associated with a haem group containing iron (II) ions
16
Q
Oxygen dissociation curves
A
Further to the left, greater affinity for oxygen ( takes it up readily but releases it less readily)
Further to the right; lower affinity for oxygen (takes up less readily but releases it more easily)
17
Q
Low oxygen environments include…
A
High altitude Underwater Burrows In the uterus This also applies to myoglobin which has a high affinity for oxygen that haemoglobin does
18
Q
Effects of carbon dioxide concentration
A
Greater concentration of carbon dioxide, the more readily haemoglobin releases its oxygen (Bohr effect)
Oxygen dissociation curve shifts to the right
19
Q
Explain why haemoglobin unloads oxygen
A
Carbon dioxide level increase
pH becomes lower so is more acidic
Haemoglobin changes shape ( ionic bonds are changed
More oxygen is dissociated
20
Q
Loading, transport and unloading of oxygen
A
Carbon dioxide is constantly removed at the gas exchange surfaces
pH is higher due to low level of carbon dioxide
Haemoglobin loads oxygen more readily
Haemoglobin has a high affinity in this state so does not release oxygen during transport
Carbon dioxide is acidic in solution so pH is lower
Shape of haemoglobin changes into one with a lower affinity for oxygen
Haemoglobin releases its oxygen into respiring tissue
21
Q
Roles of haemoglobin
A
Readily associated with oxygen at surface where gas exchange takes place as it has a high affinity here
Readily dissociate from oxygen at respiring tissues as it has a lower affinity here
22
Q
Explain the advantage of the curve being to the left in an organism in a low oxygen environment
A
High percentage saturation of haemoglobin with oxygen
At low ppO2⃣
23
Q
Explain the advantage of the curve being to the right in an organism with a high level of activity/ high metabolic rate/ high exercise
A
Haemoglobin has a lower affinity for oxygen
So releases oxygen more readily to respiring tissue
24
Q
Why do cells have to have oxygen to respire
A
To produce ATP to provide energy for processes such as active transport, muscle contraction etc
The most active cells will respire the most and therefore need the most oxygen
25
Explain how root pressure and cohesion-tension are responsible for the movement of water in xylem vessels
Salts are actively transported into the xylem
This causes the xylem to have a more negative water potential
Water enters the xylem by osmosis
Evaporation of water from the stomata causes transpiration pull
This lowers the water potential of the mesophyll
Water molecules cohere due to hydrogen bonding
And adhere to xylem walls
This pulls water up the xylem
26
Arteriole structure and function
Structure - thick muscle layer which contracts and relaxes
Function - reduces / controls blood pressure and flow into the capillaries
27
Artery structure and function
Structure - thick elastic layer, which stretches and recoils
Function- maintains a high blood pressure which is created by heart contraction
Structure - narrow lumen
Function - maintain high blood pressure
Structure - thick walls
Functions - prevents damage caused by high pressure
28
Capillaries structure and function
Rate of diffusion ( oxygen, carbon dioxide and glucose ) is increased
Structure - Numerous and branched, surface area is large
Structure - Thin endothelium, diffusion pathway is short
Structure - Narrow lumen so rbc is same size as lumen so passage of blood is slow, allows more time for diffusion to occur
Function - efficient gaseous diffusion
Constant circulation of blood maintains a steep concentration gradient
29
Vein structure and functions
Structure - Muscle layer is thin as their constriction and dilation does not control blood flow
Structure - Elastic layer is thin as pressure is low
Structure - Wall thickness is small as pressure is low, must be collapsible so can be squeezed by body muscles
Structure - Valves present to prevent back flow
30
The body makes more tissue fluid over a day that it can reabsorb. What happens to the excess
The excess is drained by the lymph vessels
| Accumulation of fluid may lead to tissue swelling (oedema)
31
Formation, reabsorption and drainage of tissue fluid
High hydrostatic pressure at the arteriole end of the capillary
Forces water out through the thin capillary walls into tissue
Plasma proteins are too large too pass through the capillary wall
So they become more concentrated in the blood
This makes the water potential inside the capillary more negative
Compared to the less negative tissues
Water moves back into the capillary by osmosis
Along a water potential gradient
The hydrostatic force outside the capillary also helps to push water back in
32
Why a person experiencing high blood pressure may get swelling?
Hydrostatic pressure of the blood is high so more water is forced out of arteriole end of capillary
Some tissue fluid accumulates as not all of it can be reabsorbed
33
Why a starving person may get swelling
Fewer plasma proteins in the blood
So concentration gradient is not as steep and inside of capillary is less negative
Therefore less water can be reabsorb into the capillary by osmosis
34
Features of binomial system
Universal system
Generic names indicates the genus the organism belongs to
Specific names denotes the particular species
35
Gravity pulls tissue fluid down so it tends to accumulate in ankles and feet then...
Feet have very few lymph vessels
Contraction of body muscles surrounding the lymph vessels squeeze the lymph back to the chest where it can be drained and eventually excreted
36
Use cohesion-tension theory to explain why the presence of an air bubble in a xylem vessel blacks the movement of water
```
The presence of the air bubble breaks the continuous column of water
And prevents cohesion of water molecules
Water in the xylem is under tension
Due to transpiration from leaves
The air bubble inhibits this tension
```
37
Explain how active transport of mineral ions into xylem vessels results in water entering and being moved up the tissue
The water potential in the xylem is made more negative
By the active transport of ions into the xylem
This establishes a water potential gradient
So water moves from an area with less negative water potential to an area with a mo negative water potential
By osmosis
This increases pressure in the xylem
38
Explain how after enters a plant root from the soil and travels through to the endodermis
Water enter root hair cells
By osmosis
As the active uptake of ions into the roots create a water potential gradient
I.e. the root has a moe negative water potential
Water moves through the root cortex
Via the cell walls - the apoplastic pathway or via the cell cytoplasm - the symplastic pathway
39
Using Fick's law to explain how the structural adaptation of xerophytes reduce the rate of water diffusion
Ficks law states that the rate of diffusion is proportional to the surface area times the concentration gradient divided by the length of the diffusion pathway
Xerophytes have a reduced number of stomata
This decreases the surface area
These plants also have a waxy cuticle
This increases the length of the diffusion pathway
These features mean that the water potential gradient is reduced
So less water is lost it the atmosphere
40
Factors affecting transpiration
Light - stomata open in the light for photosynthesis therefore an increase in light intensity increases transpiration rate
Temperature - increase in temperature increases kinetic energy and decreases the water potential of the air therefore increases transpiration rate
Humidity - increase of water molecules in air decreases the water potential gradient therefore an increase in humidity decreases transpiration rate
Air movement - an increase in air movement increases the rate of diffusion if water molecules out of the stomata and therefore increases transpiration rate
41
What can a potometer for?
To calculate rate of transpiration by measuring the uptake of water on a mm or cm scale over a set amount of time
42
Why cut the shoot and connect to the potometer under the water
To prevent air entering, to maintain a continuous water column
43
What measurements would have taken in order to calculate rate of water uptake in cm^3 min^-1
Time
Distance moved in cm
Radius/ diameter of capillary tube
44
Explain how evaporation of water from the leaves causes the water to move upwards
The water potential in the mesophyll becomes more negative
Water moves out of the xylem by osmosis
And is evaporated from the open stomata
This creates a transpiration pull
Caused by cohesion of the water molecules to each other
And adhesion to the xylem wall
45
Why might the rate of water uptake NOT be equivalent to the rate of transpiration
Water used in photosynthesis
Water produced by respiration
May be used in tissue to support the stem
46
Limiting water loss in xerophytes
Thick waxy cuticle to increase diffusion pathway
Rolled up leaves to decrease surface area for diffusion
Hairy leaves to trap a layer of moisture and decrease water potential gradient
Sunken stomata to trap moist air and reduce water potential gradient
Reduced surface area to volume ratio
47
Describe the structure if cellulose
Made of molecules of beta glucose
Joined together by condensation reactions between hydroxyl groups
Glycosidic bonds form
Polymer chains are unbranched and join together by numerous hydrogen bond cross bridges
Molecules are grouped together into microfibrils
The numerous hydrogen bonds give cellulose high tensile strength
48
Functions of cellulose cell wall
To provide mechanical strength to prevent cell bursting under the pressure created by osmotic entry of water
To give strength to the plant for support
To allow water to pass along it and contribute to the movement of water through the plant
49
Comparison of starch, cellulose and glycogen
Starch and glycogen consists of chains of alpha glucose
Cellulose consists of chains of beta glucose
All molecules have glucose joined by glycosidic bonds in a condensation reaction
Starch is made up of C1-4 linkages and C1-6 linkages
Glycogen has more 1-6 linkages that starch and therefore is more branched
Cellulose forms microfibrils joined by hydrogen bonds
50
Hierarchy of classification (taxonomy)
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Kingdom
|
Phylum
|
Class
|
Order
|
Family
|
Genus
|
Species
```
51
Roles of starch
Insoluble therefore does not affect osmotic movement of water in and out of cells
Insoluble so does not easily diffuse out of cells - good for storage
Compact so lots can be stored in a small place
When hydrolysed it forms alpha glucose which is easily transported
52
What do members of a species have in common
They are similar to one another but different from members of other species
They are capable of breeding to produce living, fertile offspring
53
The structure of cellulose is related to its role in plant cell walls. Explain how
Long, straight (unbranched) chains of glucose
Joined by hydrogen bonds
To form microfibrils
Which provide rigidity / strength / support
54
Explain what is meant by hierarchy
Groups within larger groups
| No overlap
55
What is phylogenetic tree
A diagram showing evolutionary relationships between organisms
56
Causes of variation
Random mutations in DNA due to a chance event producing a useful protein
Meiosis (crossing over and independent assortment)
Fusion of gametes during sexual reproduction
57
Removal of chance from sampling procedures
Use a large sample size, as it is more representative
Statistically analyse the data collected
You would also need to remove bias by conducting a random sample
Also need to repeat to achieve concordancy which make your results more reliable this then relates to standard deviation
58
Standard deviation
The standard deviation, the greater the variation about the mean
Results at more widespread and so are less reliable
59
Genetic bottlenecks
A chance event e.g. Natural disaster, may cause a population to drop in number dramatically
The survivors posses a smaller variety of alleles than the original population
So the genetic diversity is less
As the individual breeds the genetic diversity of the new population is restricted
60
Selective breeding
Individuals with desired characteristics are selected and used to parents the next generation with the same characteristics
Offspring that do not exhibit the desired characteristics are killed or prevented from breeding
Alleles for unwanted characteristics are breed out of the population
This leads to reduced genetic diversity
61
Founder effect
Occurs when a few individuals from a population colonise a new region
Alleles carried by the individuals may not be representative of the original population
Therefore they show less genetic diversity
The few individuals then give rise to a genetically different population
62
How are proteins compared using immunology
Serum protein from species A is injected into species B
Species B produces antibodies specific to the antigen sites on the protein from species A
Serum is extracted from species B (contains antibodies specific to the antigens from species A)
Serum from species B is mixed with serum from the blood of a third species C
Antibodies respond to their corresponding antigens on the protein in the serum of species C
A precipitate forms - the greater the number of similar antigens, the more precipitate is formed and the more closely the species are related
63
Describe how comparisons of biological molecules in 2 species could be used to find out if they are closely related
Compare DNA
sequence of bases
DNA hybridisation
Break hydrogen bonds
Mix DNA strands of the two species
Temperature required to separate indicates relationship (higher temperature means that they are more closely related)
Compare protein
Primary structure / sequence of amino acids
Inject serum from species A into an animal
Obtain antibodies from this animal
Add antibodies to species B
Amount of precipitate indicates a relationship ( more precipitate means they are more closely related)
64
Why might comparing the base sequence of a gene provide more information than comparing the amino acid sequence for which the gene codes
Because of the triplet code there are more bases than amino acids
There may be introns - areas of non coding DNA
same amino acids may be coded for by more than be triplet
I.e. code is degenerate
65
What is DNA hybridisation
DNA from each species is extracted, purified and cut into short sections
DNA from one species is radioactivity labeled and to mixed with the unlabelled DNA from the other species
Mixture is heated to separate the strands then cooled to allow them to recombine
Some of the newly formed double strands are made up of one strand from each species (these are hybrids and can be identified because 50% of their DNA is radioactively labeled)
Hybrid strands are separated and the temperature is increased in stages
The degree to which the two strands are linked is measured
If the two species are closely related the will be many complementary bases and therefore many hydrogen bonds (the greater the number of hydrogen bonds, the stronger the hybrid will be)
The stronger the hybrid, the higher the temperature needed to separate them
The higher the temperature at which the hybrid splits, the more closely the two species are related
66
How do mutations result in different characteristics?
Mutations change the base sequence of DNA
This may change the sequence of triplets (codons)
That code for amino acids
As a result the amino acid sequence may change
Enoch could affect the structure and function of the protein
If this protein is an enzyme then the change may affect the metabolism of the organism and therefore other characteristic
67
Why is courtship behaviour necessary
To recognise members of their own species ( to produce fertile offspring)
To identify a mate that is capable of breeding and recognition of opposite gender
To form a pair bond leading to successful raising of offspring
To synchronise mating so it takes place with maximum probability of the sperm and egg meeting ( indicate of fertility)
Stimulate release of gametes
68
What is the difference between horizontal and vertical gene transmission
Vertical is where genes are passes from parents to offspring within the same species
Horizontal is where genes are passed from one species to another
69
How do antibiotics work
Some antibiotics prevent the formation of the bacterial cell wall
By inhibiting the synthesis of peptide cross linkages
Water enters the bacterium by osmosis
So the bacterium swells and cell lysis occurs
70
How do bacteria become resistant to penicillin
A chance mutation results in the production of penicillinase
This enzyme is able to prevent the breakdown of cell walls by penicillin by destroying the penicillin
Therefore the enzyme was able to prevent osmotic lysis
71
What are the implications of antibiotics resistance
TB ( people who have TB may have to take a long course of antibiotics but there is a danger that they will stop taking them when they start to feel better - this means the most resistant strains may not be killed and so may be passed on. Hence a cocktail of 4 drugs is usually used)
MRSA ( a strain of the Staphylococcus bacterium that is resistant to one or more antibiotics - is a danger to vulnerable people, transmission higher in crowded conditions e.g. Hospitals, resistant strains develop more easily in hospitals where lots of antibiotics are used)
72
What are the reasons for the occurrence of resistance
Antibiotics are used to treat minor ailments with short lived symptoms
Antibiotics are sometimes used to treat secondary infections associated with viral disease
Patients do not always complete the full course
Patients stockpile used antibiotics from previous infections and may self proscribe
Doctors accept patients demands
Antibiotics are used to treat minor ailment in domestic animals
Antibiotics are used to increase productivity in farm animals or can be used to prevent disease In intensive conditions
73
What is biodiversity?
Comprised of
Species diversity - different number of species and number of individual of each species with a community
Genetic diversity - variety of genes possessed b the individuals that make up one species
Ecosystem diversity - range of different habitats within a particular area
74
What is species diversity?
Comprised of
The number of different species in a given area
The proportion of the community that is made up of an individual species
75
How genes transfer genes by conjugation
One bacterium produces a thin protection that forms a conjugation tube when it meets another cell
Donor cell replicated its plasmid
Circular DNA is broken into a linear strand
Linear strand passes down the conjugation tube to the other cell
Recipient cell acquires genes from the donor and therefore new characteristics
76
Impacts of agriculture
Farmers select species for qualities that make them more productive
Number of species and genetic variety are reduced
Pesticides are used to exclude any species that compete with the desired species for light, water, food and mineral ions
Species diversity index is low
77
Impact of deforestation
This is the permanent clearing of forests and the conversion of land to other uses e.g. Grazing
This reduced species diversity
78
what is the difference between a nucleotide and nucleic acid? (2)
A nucleotide is a monomer
| Nucleic acid is a polymer
79
Replication of DNA (4)
Double helix unzips
Catalysed by helicase
Hydrogen bonds break
Free DNA nucleotides in the nucleus complementary base pair with exposed bases on both strands
DNA polymerase joins nucleotides together on new strands (catalyse formation of ester bonds)
Results in the formation of identical strands
80
Explain why it may be more useful to calculate index of diversity than to record only the number of species present
Measure the number of individuals of each species and the number of species
Some species may be present but only in small numbers
81
Key features of DNA
Stable so can be passed on from generation to generation
Hydrogen bonds between strands are easily broken for DNA replication
Large so can carry a lot of genetic information
Base pairs are contained within the helix and are protected from corruption by the strong sugar phosphate backbone
Complementary base pairs allow the synthesis of an identical daughter molecule
82
Important features of the genetic code (4)
It is non overlapping (specific start and stop codons)
It is degenerate (some amino acids are coded for by more than one codon)
It is read in only one direction
It is universal - the same codes apply to all organism
83
Definition of a gene (1)
A section of double stranded DNA coding for a single polypeptide
84
What does semiconservative replication means? (3)
Two new molecules are formed which are exact copies of the original
One of the chains in each new molecule was present in the original molecule
The other chain is newly synthesised from free nucleotide
85
Definition of an allele
One alternative form of a gene
86
What are non coding sections of DNA called?
Introns
87
Definition of a triplet code
Three bases in a particular sequence code for one amino acid
88
If you are given the number of amino acid and asked to calculate the minimum number of DNA bases needed to calculate the minimum number of DNA bases what do you do?
X the number of amino acids by 3
89
Definition of a locus
The position of a particular allele on a chromosome
90
Relationship between DNA and protein
DNA has a specific sequence of bases
Arranged into specific codons (triplet)
Each codon codes for one amino acid
The ribosome reads the code and arranges the amino acids in the correct order (determined by the DNA sequence)
Peptide bonds form between amino acids making a polypeptide chain
This is then folded to make a protein with specific tertiary structure
91
Chromosome movement during meiosis
In first division, homologous chromosomes pair up
Equivalent portions of chromatids may cross over
Homologous pairs separate during meiosis 1, with one chromosome from each pair going into the two daughter cells
This happens randomly and is called independent segregation
Chromatids move apart during anaphase and of the second meiotic division
After the second division, four haploid daughter cells are formed with half the amount of DNA/ chromosomes as the original parent cell
92
Explain how a chain in base sequence may result in the production of a non functional enzyme (4)
Changes sequence of amino acids
Changes shape of active site (affects tertiary structure)
Substrate may no longer be complementary
Enzyme substrate complexes cannot form
93
How a mutation may result in a non functional protein (5)
DNA bases sequence changes
Codons change
So amino acid sequence changes
Secondary structure changes - bonds form in different places
Tertiary structure changes, as folding pattern has changed
94
How does DNA control the phenotype of an organism?(3)
DNA control the production of enzymes
Enzymes control metabolic pathways
Metabolic pathways influence the phenotype of an organism
95
Stages of cell division
Interphase - cells grows more cytoplasm; DNA replication; organelle replication; build up of ATP (G1, S, G2)
Prophase - chromosomes condense (shorter and fatter); nuclear envelope disappears; spindle (protein fibre) forms in the cell
Metaphase - spindle fibres attach to chromosomes at centromeres; chromosomes line up on equator of spindle
Anaphase - spindle fibres contract (shorten) and pull sister chromatids towards opposite ends of the spindle
Telophase - new nuclear envelope forms; chromosomes uncoil
Cytokinesis - cytoplasm divides and new cell membrane forms
96
Percentage increase
New value - original value. X 100
-------------------------------
Original value
97
If you are given the number of bases/base sequence and are asked to calculate the number of amino acids coded for, what do you do?
Divide the number of bases by 3
98
Preparing a mitotic squash
Cut end tip off growing root
Add aceto orcein stain
Squash
99
Why do you follow the steps to preparing mitotic squash
Root tip end has fast growing cells, dividing by mitosis
Stain to make chromosomes visible
Squash to get a thin tissue layer letting enough light through for the optical microscope
100
Similarities and differences between mitosis and meiosis
Meiosis produces gametes; mitosis produces other body cells
Meiosis produces cells with haploid number of chromosomes; mitosis produces cells with diploid number of chromosomes
Meiosis produces cells that are genetically different; mitosis produces cells that are genetically identical
Both go through prophase, metaphase, anaphase and telophase
Meiosis 2 is the same as mitosis - both involve the separation of sister chromatids
Meiosis involves the separation of homologous pairs; mitosis does not have homologous pairs of chromosomes
101
Purpose of mitosis
Produces identical body cells for growth and repair of tissues
102
Mutations
The change in alleles may change the base sequences in the DNA
So the codons change
So the amino acid sequence changes
So the primary and tertiary protein structure may also change
This is how we get genetic variation
103
Definition of cancer
Rapid and uncontrollable cell division by mitosis
104
Drugs used to treat cancer
Drug to prevent DNA replication
Drug to prevent the spindle fibres from attaching
They are both used to inhibit cell division therefore cell division slows down
105
What is the difference between a tissue and an organ?
A tissue is a group of similar cells organised to carry out a specific function
An organ is a combination of tissues that a coordinated to preform a variety of functions
106
What is cell differentiation?
The process of a cell becoming specialised in structure to carry out a specific role
107
How does meiosis produce genetic variation? (4)
Crossing over during meiosis 1 produces new combinations of alleles
Independent segregation of homologous chromosomes during meiosis 1 means chromosomes line up in different
combinations
Random gamete fusion - every sperm is different???
108
An overlap in standard deviation means that...
We can't make a conclusion about the data
109
Points to consider for evaluation question
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Sample size
Repeats
Scientists vested interest
Peer reviewed
Human experiments if for humans
Control experiment
```
110
Standard deviation
The bigger the value +/- mean, the greater the standard deviation so the more variation there is in the data
The smaller the value +/- mean, the lower the standard deviation so the less variation there is in the data
111
Causes of accumulation of tissue fluid
Blockages of lymph vessels can result form some bacterial infections and this would also lead to excess tissue fluid and swelling
There are some metabolic diseases which could lead to low levels of plasma proteins - therefore low re-adsorption
Gravity pulls lymph fluid down
112
Comparison of Mitosis and Meiosis
Meosis
Occurs only in reproductive (sex) cells
Chromosome number reduces to half, i.e., haploid (n), hence it is reductional division
Four daughter cells are produced
Consists of two sub-divisions: Meiosis - I and Meiosis - II each involving four phases. Prophase - I is again subdivided into five sub-stages
Crossing over takes place
Daughter cells have chromosomes with combined genetic material from both parents i.e., genetic variability occurs
Mitosis
Occurs in all somatic cells
Chromosome number remains same, i.e., diploid (2n), hence it is equational division
Two daughter cells are produced
One cell division involves four phases
No crossing over
Daughter cells have identical chromosomes to parent cell, i.e., genetic material remains constant
