Summary Flashcards From Website

Question 1

What is the difference between interspecific variation and intraspecific variation?

Answer 1

Interspecific = variation that exsists between different species. E.g. the difference between horses and ducks.

Intraspecific = The differences that occur within a species e.g. the length of giraffes necks

Question 2

Explain the two factors that cause variation

Answer 2

1) genetic = individuals within a species can have different versions of those genes called alleles. The alleles an organism has make up its genotype. Different genotypess result in variation in phenotype - the characteristics displayed by an organism. For example eye colour, or blood type.

Environmental = The appearance (phenotype) of an invidividual is also affected by the environment. For example plant growth in affected by the amount of minerals available in the soil or in identical twins, they have the same alleles may have had different illnesses in their childhood or if they grew up in different areas, have different accents.

Question 3

Why does the sample have to be random when studying variation and give an example on how they make it random?

Answer 3

To make sure the sample isn’t biased.

If you were looking at plant species in a field you could pick random sample sites by dividing the field in a grid and using a random number generator to select co ordinates

Question 4

What does the standard deviation of data tell us?

Answer 4

It tells you how much the values in a single sample vary, its a measure of the spread of values about the mean.

A large standard deviation means the values in the sample vary a lot. A small standard deviation tells you most of the sample data is round the mean value so varries little.

Question 5

What are the three main components of nucleotides?

Answer 5

1) A deoxyribose sugar (stays the same)
2) a phosphate group (stays the same)
3) nitrogenous base (varies)

Question 6

Describe how DNA is different in Eukaryotic cells and prokaryotic cells

Answer 6

Prokaryotic cells = DNA molecules are shorter and circular, it isn’t wound around proteins

Eukaryotic cells = The DNA is linear, really long and wound around proteins.

Question 7

How are Nucleotides joined together?

Answer 7

1) DNA nucleotides join together to form polynucleotide strands
2) The nucleotides join up between the phosphate group of one nucleotide and the sugar of another creating a sugar-phosphate backbone
3) Two DNA polynucleotide strands join together by hydrogen bonds between the bases
4) Each base can only join with one particular partner - this is called specific base pairing
5) Adenine always pairs with thymine and guanine always pairs with cytoside
6) The two strands wind up to form the DNA double-helix

Question 8

How can a mutation result in a non-functional enzyme?

Answer 8

1) mutations are changes in the base sequence of an organisms DNA
2) mutations produce new alleles of genes
3) A gene codes for a particular protein, so if the sequence of bases in a gene changes, a non-functional or different protein could be produced.
4) All enzymes are proteins, if theres a mutatio in a gene that codes for an enzyme, the enzyme may not fold up properly. There will be a change in the enzymes secondary and tertiary structure and the active site will be the wrong shape which will end up in a non-functional enzyme.

Question 9

What is an intron?

Answer 9

Sections of DNA which don’t code for amino acids.

Introns are removed during protein synthesis.

Question 10

What is a homologous pair of chromosomes?

Answer 10

Pairs of matching chromosomes
In a homologous pair, both chromosomes are the same size and have the same genes although they could have different alleles.

Question 11

Explain the two ways meiosis produces variation

Answer 11

1) crossing over of chromotids = The crossing over of chromotids in meiosis I neabs that each of the four daughter cells formed from meiosis contrain chromatids with different alleles
2) Independent assortment of chromosomes = The four daugher cells formed from meiosis have completley different combinations of chromosomes, All your cells have a combination of chromosomes, half from your mum (maternal) and half from your dad (paternal) When the gametes are produced, different combinations of those maternal and paternal chromosomes go into each cell. This is called independent assortment of chromosomes.

Question 12

Explain the process of meiosis

Answer 12

1) The DNA unravels and replicates so there are two copies of each chromosome called chromotids.
2) The DNA condenses to form double-armed chromosomes, made from two sister chromotids
3) Meiosis I - the chromosomes arrange themselves into homologous pairs
4) These homologous pairs are then seperated halving the chromosome number
5) Meiosis II - the pairs of sister chromotids that make up each chromosome are seperated
6) four haploid cells that are genetically different from each other are produced.

Question 13

Identify two arguments against and two arguments for selective breeding.

Answer 13

Arguments for selective breeding:

1) It can produce high yielding animals and plants
2) It can be used to produce animals and plants that have increased resistance to disease

Arguments against selective breeding:

1) It can cause health problems to the animals
2) It reduces genetic diversity

Question 14

How does the founder effect reduce genetic diversity?

Answer 14

The founder effect is when just a few organisms from a population start a new colony. Only a small number of organisms have contributed their alleles to the gene pool. A narrower range of alleles lead to lower genetic diversity.

Question 15

How do genetic bottlenecks reduce genetic diversity?

Answer 15

A genetic bottle neck is an event that causes a big reduction in a population e.g when a large number of organisams within a population die before reproducing. This reduces the number of different alleles in the gene pool and so reduces genetic diversity. The survivors reproduce and a larger population is created from a few individuals.

Question 16

How does selective breeding reduce genetic diversity?

Answer 16

Selective breeding leads to a reduction in genetic diversity - once an organism with the desired characteristics has been produced, only that type of organism will continue being bred,.
It results in a type of genetic bottle neck as it reduces the number of alleles in the gene pool.

Question 17

How is oxygen carried round the body by haemoglobin?

Answer 17

1) Haemoglobin has a high affinity for oxygen - each molecule can carry four oxygen molecules
2) In the lungs, oxygen joins to haemoglobin in red blood cells to form oxyhaemoglobin
3) This is a reversible reaction - when oxygen leaves oxyhaemoglobin near the body cells, it turns back to haemoglobin.

Question 18

How does the carbon dioxide concentration affect oxygen unloading?

Answer 18

1) when cells respire they produce carbon dioxide, which raises the pCO2
2) This increases the rate of oxygen unloading - the dissociation curve shifts down. The saturation of blood with oxygen is lower for a given pO2 meaning that more oxygen is being released
3) This is caused the Bohr effect

Question 19

How is haemoglobin different in different organisms?

Answer 19

1) organisms that live in environments with a low concentration of oxygen have haemoglobin with a higher affinity for oxygen than human haemoglobin - the dissociation curve is to the left of ours
2) Organisms that are very active and have a high oxygen demand have haemoglobin with a lower affinity for oxygen than human haemoglobin - the curve is to the rightof the human one.

Question 20

Explain how haemoglobin load and unload in the body?

Answer 20

1) The partial pressure of oxygen is a measure of oxygen concentration. The greater the concentration of dissolved oxygen in cells, the higher the partial pressure
2) Similarly , the partial pressure of carbon dioxide is a measure of the concetration of CO2 in a cell.
3) Haemoglobins affinity for oxygen varies depending on the partial pressure of oxygen.
4) oxygen loads onto haemoglobin to form oxyhaemoglobin where theres a high PO2, oxyhaemoglobin unloads its oxygen where theres a lower pO2
5) oxygen enters blood capillaries at the alveoli in the lungs. Alveoli have a high PO2 so oxygen loads onto haemoglobin to form oxyhaemoglobin
6) when cells respire, they use up oxygen - this lowers pO2, Red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads its oxygen.
7) The haemoglobin then returns to the lungs to pick up more oxygen.

Question 21

Describe the difference between starch, glycogen, and cellulose

Answer 21

Starch = 1) the main energy storage material in plants
2) Its a mixture of two polysaccharides of alpha-glucose - amylose and amylopectin.
Amylose = long unbranched chain = a coiled structure, this makes it compact which makes it good for storage
Amylopectin = a long branched chain = its side branches allow enzymes to get at the glycosidic bonds easily. Glucose can be released quickly.
3) Starch is insoluble so it doesnt cause water to enter cells by osmosis

Glycogen = 1) the main storage material in animals

2) branched - stored glucose can be released quickly
3) compact molecule - good for storage

Cellulose =1) the major component of cell walls in plants

2) cellulose is made of long, unbranched chains of beta-glucose
3) bonds between sugars are straight so cellulose chains are straight
4) Cellulose chains are linked together by hydrogen bonds to form strong fibres called microfibrils. This means cellulose provides strcutural support for cells.

Question 22

Give three structures that plant cells have that animal cells don’t have

Answer 22

1) rigid cell wall = made of cellulose, it supports and strengthens the cell
2) permanant vacuole = contains cell sap, a weak solution of sugar and salts
3) chloroplasts - where photosynthesis occurs, which makes food for the plant. They contain a gren substance called chlorophyll.

Question 23

Describe what chloroplasts are

Answer 23

Chloroplasts are surrounded by a double membrane and are also have membranes inside called thylakoid membranes. These membranes are stacked up in the chloroplast to form grana.

Grana are linked together by lamellae - thin, flat pieces of thylakoid membrane.

Some parts of photosynthesis happen in the grana and other parts happen in the stroma.

Question 24

Describe the cell cycle

Answer 24

1) The cell cycle starts when a cell has been produced by cell division and ends with the cell dividing to produce two identical cells
2) The cell cycle consists of a period of cell growth and DNA replication, called interphase and a period of cell division called mitosis.
3) Interphase (cell growth) is subdivided into three seperate growth stages. These are called G1, S and G2

Question 25

Describe how the DNA is replicated

Answer 25

1) the enzyme DNA helicase breaks the hydrogen bonds between the two polynucleotide DNA strands. The helix unzips to form two single strands.
2) Each original single strand acts as a template for a new strand. Free-floating DNA nucleotides join to the exposed bases on each original template strand by specific base pairing - A with T, and C with G
3) The nucleotides on the new strand are joined together by the enzyme DNA polymerase. Hydrogen bonds form between the bases on the original and new strand
4) Each new DNA molecule contains one strand from the original DNA molecule and one new strand.

Question 26

Describe the stages of mitosis

Answer 26

Interphase = DNA replicates
chromosomes invisible

Prophase = chromosomes become visible
nucleolus disappears

Metaphase = spindle forms
chromosomes line up on equator of cell

Anaphase = chromatids are pulled towards poles
spindle fibres attached to chromatids contract

Telophase = spindle disintegrates
nucleur envelope reforms

Question 27

Define what an organ is.

Answer 27

An organ is a group of different tissues that work together to perform a particular function

Question 28

Explain how fish are adapted for gas exchange.

Answer 28

1) Each gill is made of lots of thin plates called gill filaments, which give a big surface area for exchange of gases
2) The gill filaments are covered in lots of tiny structures called lamellae, which increases the surface area even more.
3) The lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion
4) Blood flows through the lamellae in one direction and water flows over in the opposite direction. This is called a counter-current system. It maintains a large concentration gradient between the water and the blood.

Question 29

Explain how insects are adapted for gas exchange.

Answer 29

1) insects have microscopic air-filled pipes called tracheae which they use for gas exchange.
2) Air moves into the tracheae through pores on the surface called spiracles
3) Oxygen travels down the concentration gradient towards the cells. Carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere.
4) The tranchae branch off into smaller tracheoles which have thin, permable walls and go to individual cells. This means that oxygen diffuses directly into the respiring cells - the insects circulatory system doesn’t transport o2
5) insects use rhythmic abdominal movements to move air in and out of spiracles.

Question 30

Explain how single-celled organisms are adapted for gas exchange

Answer 30

1) They absorb and release gases by diffusion through their outer surface
2) They have a relativley large surface area, a thin surface and a short diffusion pathway.

Question 31

Give examples of adaptations for xerophytic plants

Answer 31

1) stomata sunk in pits which trap moist air, reducing evaporation
2) curled leaves with the stomata inside, protecting them from wind
3) a layer of ‘hairs’ on the epidermis to trap moist air round the stomata, reducing the concentration gradient of water
4) A reduced number of stomata, so there are fewer places for water to escape
5) waxy, waterproof cuticles on leaves and stems to reduce evaporation

Question 32

Explain the differences between arteries, capillaries and veins.

Answer 32

Arteries = carry blood from the heart to the rest of the body. thick muscular wall, Thick elastic wall, relatively small lumen, blood under high pressure and valves

Capillaries = No muscle, No elastic tissue, relativley large lumen, blood under low pressure, no valves

Veins = Thin muscle wall, little elastic tissue, relativley large lumen, blood under low pressure, semilunar valves.

Question 33

Which components of blood do not normally enter the tissue fluid?

Answer 33

Plasma proteins - red blood cells or big proteins as they are too big to be pushed through the cappilary walls

Question 34

Which blood vessel carries blood

a) from the heart to the lungs
b) from the intestine to the liver

Answer 34

a) pulmonary artery

b) hepatic portal vein

Question 35

Explain how tissue fluid is formed and how it is returned to the circulation

Answer 35

1) At the start of the capillary bed, nearest the arteries, the pressure inside the cappilaries is greater than the pressure in the tissue fluid. The difference in pressure forced the fluid out of the cappilaries and into the spaces forming tissue fluid (pressure filtration)
2) As fluid leaves, the pressure reduced in the capillaries - so the pressure is much lower at the end of the cappilary bed thats nearest to the veins.
3) Due to fluid loss, the water potential at the end of the cappilaries nearest the veins is lower than the water potential in the tissue fluid - so some water re-enters the cappilaries from the tissue fluid at the vein end by osmosis

Question 36

Identify four factors that affect transpiration rate and explain how they affect it.

Answer 36

Light = the lighter it is, the faster the transpiration rate. This is because the stomata open when it gets light. When its dark the stomata are usaully closed so theres little transpiration

Temperature = The higher the temperature, the faster the transpiration rate. Warmer water molecules have more energy so they evaporate from the cells inside the leaf faster. This increases the concentration gradient between the inside and the outside of the leaf making water diffuse out of the leaf faster

Humidity = The lower the humidity, the faster the transpiration rate. If the air around the plant is dry, the concentration gradient between the leaf and the air is increased, which increases transpiration

Air movement = The windier it is, the faster the transpiration rate. Lots of air movement blows away water molecules from around the stomata. This increases the concentration gradient, which increases the rate of transpiration.

Question 37

Explain what root pressure and the cohesion tension theory do.

Answer 37

Root pressure = When water is transported into the xylem in the roots, it creates pressure and shoves water already in the xylem furthur upwards. This pressure is weak and couldn’t move water to the top of bigger plants by itself. But it helps, especially small plants with leaves still developing

Cohesion tension theory = water evaporates from the leaves, this creates tension which pulls more water into the leaf. Water molecules are cohesive so when some of them are pulled into the leave, others follow. This means that the whole column of water in the xylem, from the leaves down to the roots, move upwards. Water enters the stem through the roots.

Question 38

What is taxonomy?

Answer 38

Taxonomy is the science of classification. It involves naming and organising organisms into groups based on similarities and differences.

Question 39

What is the order of the taxonomic hierachy?

Answer 39

Kingdom
phloem
class
order
family
genus
species

Question 40

Why cant you define organisms as members of a distinct species

Answer 40

Because you cant always see their reproductive behaviour for the following reasons:
they’re exstinct
they reproduce asexually
there are practical and ethical issues

Question 41

What is phylogenetics?

Answer 41

The study of the evolutionary history of groups of organisms, It tells us whos related to who and how closely related they are

Question 42

Describe the two ways DNA can be compared?

Answer 42

DNA sequencing = looking at the order of bases in each. Closely related species will have a higher percentage of similarity in their DNA base order. DNA sequence comparison has led to new classification systems for plants

DNA hybridisation = used to see how similar DNA is without sequencing it. Heres how its done:
DNA from two different strands is collected,seperated into single strands and mixed together. Where the base sequences of the DNA are the same on both strands, hydrogen bonds form between the base pairs by specific base pairing. The more DNA that hybridise together, the more alike the DNA is.
The DNA is then heated to seperated the strands again. Similar DNA will have more hydrogen bonds holding the two strands together so a higher temperature will be needed to seperate the strands.

Question 43

Describe the two ways proteins can be compared?

Answer 43

Comparing amino acid sequence = The sequence of amino acids in a protein is coded for by the base sequence in DNA. Related organisms have similar DNA sequences and so similar amino acid sequences have their proteins.

Immunological comparisons = Similar proteins will bind the same antibodies

Question 44

How can courtship behaviour be used to classify species?

Answer 44

Courtship behaviour is carried out by organisms to attract a mate of the right species
Only members of the same species will do and responds to that courtship behaviour. This prevents interbreeding and so makes reproduction more successful (as mating with the wrong species won’t produce fertile offspring)
Courtship behaviour can be used to classify organisms. The more closely related species are, the more similar their courtship behaviour. An Example include:
crickets make sounds that are similar to morse code, the code being different for different species.

Question 45

What is osmosis lysis?

Answer 45

1) The antibiotic inhibit enzymes that are needed to make the chemical bonds in the cell wall.
2) This prevents the cell from growing properly and weakens the cell wall
3) Water moves into the cell by osmosis
4) the weakened cell wall can’t withstand the increase in pressure and bursts

Question 46

What is the difference between horizontal and vertical gene transmission?

Answer 46

Vertical gene transmission = Bacteria reproduce asexually, so each daughter cell is an exact copy of the parent. This means that each daughterr cell has an exact copy of the parents cells genes, including any that give it antibiotic resistance. Genes for antibiotic resistance can be found in the bacterial chromosome or in plasmids. The chromosome and any plasmids are passed on to the daughter cells during reproduction.

Horizontal gene transmission = Genes for resistance can also be passed on horizontally, two bacteria join together in a process called conguation and a copy of a plasmid is passed from one cell to the other. Plasmids on to a member of the same species or a totally different species.

Question 47

How has bacterial populations evolve antibiotic resistance by natural selection?

Answer 47

1) some individuals in a population have alleles that give them resistance to an antibiotic
2) the population is exposed to that antibiotic, killing bacteria without the abntibiotic resistance allele.
3) The resistant bacteria surviver reproduce without competition, passing on the allele that gives antibiotic resistance to their offpsring.
4) After some time most organisms in the population will carry the antibiotic resistance allele

Question 48

How does deforestation decreases species diversity?

Answer 48

It directly reduces the number of trees and sometimes the number of different tree species.
It also destroys habitats so some species could lose their shelter and food source. This means that these species will die or be forced to migrate
The mirgration of organisms into increasingly smaller areas of remaining forest may temporarily increase species diversity

Question 49

What are the benefits and risks of deforestation?

Answer 49

Benefits:
wood and land for homes to be built
local areas become more developed

Risks:
diversity is reduced
less carbon dioxide is stored because there are fewer plants and trees which contributes to climate change
natural beauty is lost

Question 50

What are the ways agriculture reduces diversity?

Answer 50

1) woodland clearance
2) hedgerow removal
3) monoculture
4) pesticides
5) herbicides