cell division

Question 1

State three events that occur in G1 phase of the cell cycle

Answer 1

Cells grow and increase in size; proteins from which organelles are made are synthesised (transcribed and translated); organelles replicate

Question 2

Describe what may happen in G0 phase of the cell cycle

Answer 2

Cells may undergo apoptosis, differentiation or senescence

Question 3

state 3 cell cycle check points and briefly describe what is being checked for at each

Answer 3

G1/S - checks for size, growth factors, nutrients, DNA damage; G2/M - checks DNA has been properly replicated; spindle assembly - checks chromosomes have correctly attached to spindle fibres

Question 4

State three purpose of mitosis in life cycles

Answer 4

Asexual reproduction; growth; tissue repair; development of body plan; production of new stem cells; proliferation of lymphocytes (clonal expansion)

Question 5

Describe the main events of prophase

Answer 5

Nuclear envelope breaks down; chromatin condenses (DNA supercoils); nucleolus disappears; spindle fibres start to form from centrioles

Question 6

Describe the main events of metaphase

Answer 6

Chromosomes line up along equator (metaphase plate); spindle fibres attach through centromeres

Question 7

Describe the main events of anaphase

Answer 7

Sister chromatids pulled to opposite poles of the cell by shortening tubulin spindle fibres

Question 8

Describe the main events of telophase

Answer 8

Sister chromatids pulled to opposite poles of the cell by shortening tubulin spindle fibres

Question 9

Describe how cytokinesis differs between dividing animal cells and plant cells

Answer 9

Animal cells - cleavage furrow forms and plasma membrane is pulled inwards, splitting the cytoplasm; plant cells - vesicles assemble around metaphase plate and fuse; new plasma membrane and cellulose cell wall are laid down

Question 10

Why would we use the root tip for investigating mitosis?

Answer 10

It is the location of meristematic tissue (source of stem cells) in a plant, i.e. cells are actively dividing

Question 11

Explain why we warm the root tips in hydrochloric acid when preparing a root tip squash

Answer 11

To break the links between cellulose cell walls in plant cells; this ensures the stain penetrates the cells and binds to the chromosomes

Question 12

Which stain would we use to stain chromosomes in a root tip squash?

Answer 12

Acetic orcein, toluidine blue

Question 13

Describe and explain how erythrocytes are adapted for their function

Answer 13

Very small so have a large SA:vol (biconcave shape also ensures this) meaning oxygen can reach all regions inside the cell; well-developed cytoskeleton allows the erythrocytes to change shape and move through very narrow capillaries; no nucleus or organelles so more space for Hb molecules

Question 14

explain why a neutrophil contains many lysosomes

Answer 14

These contain hydrolytic enzymes which digest pathogens

Question 15

Describe and explain how sperm cells are adapted for their function

Answer 15

Acrosome in head contains enzymes to penetrate the egg follicle during fertilisation; many mitochondria to generate ATP for flagellar movement; large haploid nucleus in head to fertilise haploid ovum

Question 16

Describe how guard cells open in sunny conditions

Answer 16

Light energy –> ATP; ATP used to actively transport potassium ions from epidermal cells into guard cells; water potential of guard cells lowered; water moves in by osmosis and guard cells become turgid

Question 17

Describe the purpose of cytoskeleton threads and motor proteins in palisade cells

Answer 17

Moves the chloroplasts to areas of appropriate light intensity

Question 18

Describe how a root hair cell plasma membrane is adapted for transport of mineral ions

Answer 18

Contains specialised carrier proteins to transport specific mineral ions in by active transport

Question 19

Describe how cartilage is adapted for its function

Answer 19

Connective tissue that contains elastin and collagen fibres; prevents ends of bones from rubbing together

Question 20

Define the term tissue

Answer 20

A group of cells working together to perform a particular function

Question 21

State three types of muscle tissue, giving an example of where each is found

Answer 21

Skeletal - bicep/tricep etc.;
smooth - digestive tract, blood vessels;
cardiac muscle - heart walls

Question 22

Give four features of meristematic cells that means they can differentiate easily

Answer 22

Thin walls with very little cellulose; no chloroplasts; no large vacuole; divide by mitosis and have the ability to differentiate into many cell types

Question 23

Describe the differences between multipotent, pluripotent and totipotent stem cells

Answer 23

Multipotent - found in bone marrow and can form a range of different cells including blood cells; pluripotent - found in early embryos (embryonic stem cells) and can form all tissue types except extra-embryonic cells; totipotent - found in first 16 cells post-zygote and can form all tissue types including extra-embryonic tissue (e.g. placenta, umbilical cord)

Question 24

State three characteristics of stem cells

Answer 24

Undifferentiated; all genes able to be expressed; self-renewing; able to differentiate into any cell type

Question 25

Describe how meiosis produces genetic variation in the gametes produced

Answer 25

Crossing over in prophase I; independent assortment in metaphase I; independent assortment in metaphase II

Question 26

Describe the difference between anaphase I and anaphase II

Answer 26

In anaphase I, a homologous pair of chromosomes is separated so the chromosome number halves (2 haploid cells made); in anaphase II, sister chromatids of each chromosome are separated so chromosome number stays the same (haploid number maintained)

Question 27

In which stage of meiosis is the chromosome number halved

Answer 27

Anaphase/telophase I

Question 28

Explain why genetic variation is important for a population of organisms

Answer 28

More likely that some individuals are adapted to a change in the environment, so the population can survive