Biology Revision Unit 2 Apr 25Th

Front 1

three main uses of mitosis

Back 1

growth, repair, asexual reproduction

Front 2

whats the use of follicle cells?

Back 2

form protective coating

Front 3

why meiosis is so important and how it does this?

Back 3

because it creates genetic variation. it makes gametes that are genetically different.

1, crossing over of chromatids
2, independent assortment of chromosomes

Front 4

explain what crossing over is and how it leads to genetic variation?

Back 4

1, before the first division of meiosis, homologous pairs of chromosomes come together and pair up.
2, the chromatids twist around each other
3, bits of the chromatids break off and rejoin onto the other chromatid
4, the chromatids now contain different combinations of alleles
5, this means each of the four daughter cells will contain chromatids with different combinations of alleles

Front 5

explain how independent assortment leads to genetic variation?

Back 5

1, independent assortment means the chromosome pairs can split up in any way
2, so the cells produced can contain any combination of maternal and paternal chromosomes with different alleles

Front 6

describe the process of fertilisation in mammals, starting with the acrosome reaction

Back 6

1, during the acrosome reaction, digestive enzymes are released from the acrosome of the sperm
2, these enzymes digest the zona pellucida
3, allows a sperm to pass through and fuse with the cell membrane of the egg cell
4, this triggers the cortical reaction皮层反应
5, where the contents of the cortical granules are released from the egg cell
6, the chemicals from the cortical granules make the zona pellucida thick and impenetrable to other sperm
7, so that only one sperm can fertilise the egg cell
8, the sperm nucleus enters the egg cell
9, and fuses with the egg cell nucleus - this is fertilisation.

Front 7

what is extraembryonic cells?

Back 7

totipotency can produce while pluripotency can not produce. it's the cells of the placenta and umbilical cord

Front 8

describe how differential gene expression results in the production of specialised cells.

Back 8

1, all stem cells contain the same genes but not all of them are expressed/active
2, under the right conditions, some genes are activated, and others are inactivated
3, mRNA is only transcribed from the active genes
4, mRNA from the active genes is translated into proteins
5, these proteins modify the cell by changing the cell structure
6, and controlling the cell's processes
7, the changes cause the cell to become specialised
8, and they are hard to reverse.

Front 9

explain how embryonic stem cells are obtained?

Back 9

1, embryos are created in a laboratory using in vitro fertilisation
2, egg cells are fertilised by sperm outside the womb
3, once the embryos are approximately 4 to 5 days old, stem cells are removed from them
4, the rest of the embryo is destroyed

Front 10

suggest two reasons why some people are opposed to using stem cells from embryos?

Back 10

1, some people believe that fertilised embryos have a right to life from the moment of fertilisation
2, some people believe it is wrong to destroy viable embryos

Front 11

different alleles for the same gene are found in the same position on chromosomes. this position is called the?

Back 11

locus

Front 12

how smoking during pregnancy affects the birth mass of newborn babies. the results showed that women who smoked during the entire pregnancy had babies with a mean reduction in birth mass of 377 grams. but the reduction was as much as 1285 grams among women with certain genotypes. what canbe concluded about eh influence of genetic factors and environmental factors on birth mass? give evidence from the study to support your answer.

Back 12

1, environmental factors such as smoking affect birth mass
2, women who smoked showed a mean reduction in the birth mass of their babies of 377g.
3, genetic factors also affect birth mass of babies born to women who smoke.
4, the reduction in birth mass was as much as 1285g among women who smoked and had certain genotypes.

Front 13

explain what it meant niche?

Back 13

1, Niche is the role of a species within its habitat.
2, it included the organism's interactions with other living organisms
3, and its interactions with the non-living environment

Front 14

explain how natural selection can lead to adaptatioins becoming more common in a population

Back 14

1, individuals within a population show variation in their phenotypes/characteristics
2, predation, disease and competition create a struggle for survival
3, individuals with better adaptations are more likely to survive, reproduce and pass on their advantageous adaptations to their offspring
4, over time, the number of individuals with the adaptations increases
5, over generations the adaptations become more common in the population.

Front 15

the names and order of the seven levels of groups in taxonomy

Back 15

kingdom, phylum, class, order, family, genus, species

Front 16

compare the structure and function of xylem vessels and sclerenchyma fibres

Back 16

Structure:
1, both longer than they are wide
2, no cytoplasm
3, no end walls
4, made of dead cells, joined end to end
5, cell walls of both are thickened with lignin which helps to support the plant

Function:

the function of xylem vessels is to transport water and mineral ions, and provide support. the function of sclerenchyma fibres is to provide support.

Front 17

cell wall?

Back 17

Description: a rigid structure that surrounds plant cells. it's made mainly of the carbohydrate cellulose.

Function:supports plant cells.

Front 18

middle lamella?

Back 18

Description: the outermost layer of the cell

Function: this layer acts as an adhesive, sticking adjacent plant cells together. it gives the plant stability.

Front 19

plasmodesmata?

Back 19

Description: channels in the cell walls that link adjacent cells together.

Function: allow transport of substances and communication between cells.

Front 20

pits?

Back 20

Description: regioins of the cell wall where the wall is very thin. they are arranged in pairs - the pit in one cell is lined up with the pit in the adjacent cell.

Function: allow transport of substances between cells.

Front 21

chloroplast?

Back 21

Description: a small, flattened structure. It's surrounded by a double membrane, and also has membranes inside called thylakoid membranes. These membranes are stacked up in some parts of the chloroplast to form grana. Grana are linked together by lamellae - thin, flat pieces of thylakoid membrane.

Function: the site where photosynthesis takes place. Some parts of photosynthesis happen in the grana, and other parts happen in the stroma (a thick fluid found in chloroplasts)

Front 22

amyloplast?

Back 22

Description: a small organelle enclosed by a membrane. they contain starch granules.

Function: storage of starch grains. they also convert starch back to glucose for release when the plant requires it.

Front 23

vacuole and tonoplast?

Back 23

Description: the vacuole is a compartment surrounded by a membrane called the tonoplast.

Function:
1, the vacuole contains the cell sap, which is made up of water, enzymes, minerals and waste products.
2, Vacuoles keep the cells turgid - this stops plants wilting.
3, they are also involved in the breakdown and isolation of unwanted chemicals in the cell.
4, the tonoplast controls what enters and leaves the vacuole.

Front 24

describe the arrangement of cellulose microfibrils in a plant cell wall, and explain how this relates to the properties of plant fibres.

Back 24

1, the cell wall contains cellulose microfibrils in a net-like arrangement
2, the strength of the microfibrils and their arrangement in the cell wall makes plant fibres strong.

Front 25

describe secondary thickening of plant cell walls, and explain how this relates to the properties of plant fibres.

Back 25

1, it is the prouction of another cell wall between the normal cell wall and the cell membrane.
2, it is thicker, inflexible, rigid plant cell wall, has more lignin than the normal cell wall.build up as cellulose microfibrils
3, laid densely at different angles to each other, net-like
4, gives plant fibres strength.

Front 26

why plants need water?

Back 26

1, water is needed for photosynthesis
2, to maintain structural rigidity
3, transport minerals
4, regulate temperature.

Front 27

why plants need magnesium ions?

Back 27

needed for the production of chlorophyll - the pigment needed for photosynthesis.

Front 28

why plants need nitrate ions?

Back 28

needed for the prouction of DNA, proteins (including enzymes) and chlorophyll. they are required for plant growth, fruit production and seed production.

Front 29

why plants need calcium ions?

Back 29

important components in plant cell walls. they are required for plant growth.

Front 30

a new drug made from a plant extract would have to go through clinical trials. before it's made available to patients. describe this process.

Back 30

1, the first phase involves testing the drug on a small group of healthy individuals. it's done to identify any side effects, the safe dosage and how the body reacts to the drug.
2, the second phase involves testing the drug on a large group of patients. it's done to see how well the drug works.
3, the third phase involves testing the drug on a very large group of patients. it's done to compare the effectiveness of the drug with existing drugs. patients are randomly split into two groups, one which receives the new drug, and one which receives an existing treatment.

Front 31

what is biodiversity?

Back 31

1, biodiversity is the variety of living organisms in an area.
2, it includes species diversity - the number of different species and the abundance of each species in an area.
3, genetic diversity - the variation of alleles within a species (or a population of a species)

Front 32

endemism?

Back 32

endemism is when a species in unique to a single place.

Front 33

there are several species of finch that are only found on the Hawaiian islands. describe one way you could measure the biodiversity of finches within a single habitat and one way you could measure biodiversity within a single finch species.

Back 33

1, to measure the biodiversity of finches within a single habitat you could count the number of different species present in the habitat / you could find the species richness / you could count the number of different species and the abundance of each species and then used a biodiversity index to calculate species diversity
2, to measure the biodiversity within a single finch species you could find the genetic diversity / you could count the variety of phenotypes present / you could sequence the DNA of individuals and compare them with each other.

Front 34

reintroducing organisms to the wild can cause problems?

Back 34

1, reintroduced organisms could bring new diseases to habitats, harming other organisms living there.
2, reintroduced animals may not behave as they would if they had been raised in the wild.

Front 35

advantages to use seedbanks?

Back 35

1, cheaper to store seeds than to store fully grown plants
2, larger numbers of seeds can be stored than grown plants because they need less space
3, less labour is required to look after seeds than plants
4, seeds can be stored anywhere, as long as it's cool and dry. plants would need the conditions from their original habitat.
5, seeds are less likely to be damaged by disease, natural disaster or vandalism than plants.

Front 36

disadvantages to use seedbanks?

Back 36

1, testing the seeds for viability can be expensive and time-consuming
2, store all types of seed and regularly test them all for viability is expensive
3, it may be difficult to collect seeds from some plants as they may grow in remote locations

Front 37

suggest why it is better to use several explants when trying to demonstrate totipotency rather than one explant

Back 37

one explant may die, but for three this is much less likely.

Front 38

there are risks associated with stem cell treatments. give two possible risks to the person receiving the stem cell treatment

Back 38

possible infection. increased change of cancer. tumour cells developing.

Front 39

three domains have been identified based on?

Back 39

molecular phylogeny

Front 40

what's the three domains?

Back 40

bacteria, archaea, eukaryota

Front 41

in a large population of organisms, eight different alleles were found for one gene. however, when only half of the population was sampled, six different alleles were found for the same gene. suggest two possible reasons for the absence of the two alleles.

Back 41

1, alleles rare in the population
2, not sampled by chance

Front 42

three types of adaptation?

Back 42

anatomical, behavioural, physiological

Front 43

anatomical adaptation?

Back 43

a physical/structural adaptation - it may be external or internal.

Front 44

behavioural adaptation?

Back 44

a change in the behaviour of an organism to increase its survival chances.

Front 45

physiological adaptation?

Back 45

changes in the internal biochemical functioning of the organism in response to an altered environmental stimulus.

Front 46

natural selection?

Back 46

it is the selective pressure that makes it possible for certain alleles/genetic variants to be more successful in survival and reproduction than others.

Front 47

the roles of zoos in conserving endangered animals

Back 47

1, education
2, scientific research
3, captive-breeding programmes
4, reintroduction programmes

Front 48

suggest why decreasing the temperature and water content increases the length of time seeds can remain in storage?

Back 48

1, enzymes are slowed down
2, decay occurs more slowly
3, germination is inhibited

Front 49

it has been hypothesised that chloroplasts and mitochondria have a similar evolutionary origin. describe the structural aspects of these two organelles that would give supporting evidence for this hypothesis

Back 49

both have double membrane present. both have a loop of DNA.

Front 50

describe and explain how the structure of sclerenchyma fibres and the structure of xylem vessels are appropriate to their functions.

Back 50

1, for sclerenchyma, strucure: deposition of lignin in the cell walls. function: lignin is strong to aid in the support of the plant.

For xylem, the two strucural aspects: presence of lignin and that they are long hollow tubes. this allows the two functions of structural support to the plant and a continuous pipe to allow water and mineral ions to move up the stem.

Front 51

importance of water?

Back 51

1, inflating cells (turgor) which helps to keep plants upright
2, as a component of chemical reactions such as in photosynthesis
3, as the medium in which biochemical reactions occur in cells
4, as a transport liquid for mineral ions and organic molecules such as sucrose

Front 52

nitrate?

Back 52

to supply nitrogen for making proteins. DNA, RNA, and certain plant hormones

Front 53

calcium?

Back 53

to form calcium pectate in plant cell walls. to be involved in membrane permeability.

Front 54

magnesium?

Back 54

1, as a component of chlorophyll
2, to help in the formation of DNA
3, as an activator of certain plant enzymes

Front 55

describe the position of xylem in a stem?

Back 55

innermost side of a vascular bundle

Front 56

draw a plant cell and label a structure that contains calcium pectate and an organelle that requires a lot of magnesium

Back 56

drawing of cell with laabel to middle lamella for calcium pectate, plus lable to chloroplast for magnesium

Front 57

give two structural similarities and two structural differences between the polysaccharides starch and cellulose.

Back 57

similarities: both made of glucose units, joined by glycosidic bonds

differences: only starch has a-glucose/only cellulose has B-glucose. only starch can have branches.

Front 58

suggest why adding smaller masses in the investigation described above produces more accurate results than adding larger masses?

Back 58

the mass required to break the fibre is somewhere between the last mass added before it breaks and the one that caused it to break. using smaller masses means there is a smaller range between the true breaking mass and the recorded breaking mass (thereby increasing accuracy)

Front 59

compare the bonds found in starch, cellulose and cellulose microfibrils.

Back 59

all have glycosidic bonds, but starch does not have hydrogen bonds. a in starch and B in cellulose

Front 60

suggest why large numbers of patients are needed in phase 3 of a modern drug testing protocol

Back 60

1, to collect as much statistical data as possible
2, looking for rare side effects

Front 61

similarities between modern protocals and william withering's digitalis soup

Back 61

similarities:
1, both isolated a possible drug/treatment
2, both initially tested on a small number of patients and then a large goup of patients

Front 62

differences between modern protocols and william withering's digitalis soup

Back 62

1, only modern protocols test on animals before phase 1
2, only modern protocols have phase 1 testing where drug is tested on healthy people
3, only modern protocols have double blind trials, including using a placebo, undertaken to collect data for statistical analysis

Front 63

procedue of double blind trial?

Back 63

1, patients are randomly divided into two groups
2, one group receives drug/treatment and the other group receives the placebo or standard treatment
3, neither the patients nor those recording any changes in the patients know who has received the drug and who has received the placebo or standard treatment. this reduces the chances of bias.