SB2: Cells And Control

Question 1

Name the two stages of the cell cycle

Answer 1

Interphase and mitosis

Question 2

List the five stages of mitosis in order

Answer 2

• prophase
• metaphase
• anaphase
• telophase
• cytokinesis

Question 3

Describe what happens during interphase

Answer 3

The stage when the cell prepares itself for the process of cell division, and DNA replication takes place. The cell also makes more of its sub-cellular structures, and increases in size

Question 4

Describe what happens during each stage of mitosis

Answer 4

Prophase: the nucleus starts to break down and spindle fibres appear
Metaphase: the chromosomes line up across the middle of the cell
Anaphase: the separated chromosomes move away from each other
Telophase: the chromosomes arrive at opposite ends of the cell and the nucleus membrane reforms
Cytokinesis: the cytoplasm of the cell is separated as the cell membrane is pinched to divide the cell into two daughter cells

Question 5

Why is mitosis important for an organism?

Answer 5

It is a process of producing genetically identical, diploid cells, needed for growth

Question 6

What do we call cells that have one copy of each chromosome?

Answer 6

Haploid

Question 7

Name three examples of a cell with only one copy of each chromosome

Answer 7

Gametes: egg, sperm, pollen

Question 8

What do we call cells that have two copies of each chromosome?

Answer 8

Diploid

Question 9

Name an example of a cell with two copies of each chromosome

Answer 9

Any body cell (eg. Muscle, epithelial, nerve etc.)

Question 10

Fruit flys have four types of chromosomes. How many chromosomes are in a diploid fruit fly cell?

Answer 10

8

Question 11

Explain why the number of mitochondria in a cell doubles during interphase

Answer 11

So each daughter cell has enough mitochondria/ same number of mitochondria as parent cell

Question 12

What do we call the offspring from asexual reproduction?

Answer 12

Clones

Question 13

What are spindle fibres and what is their function?

Answer 13

Filaments formed in a cell during mitosis, which help to separate chromosomes

Question 14

Give a benefit of asexual reproduction

Answer 14

• produces clones
• doesn’t need two parents
• fast method of producing offspring

Question 15

Give a disadvantage of asexual reproduction

Answer 15

• does not provide variation, so a whole population could get killed by one disease

Question 16

Describe how mitosis produces genetically identical, diploid cells

Answer 16

The cell copies each chromosome to produce two sets. Each set of chromosomes move to opposite sides of the cell. The cell then splits into two cells, each with a full set of identical chromosomes

Question 17

Why is each plantlet that grows along a strawberry runner a clone?

Answer 17

Because they are genetically identical to the parent plant/ have the same chromosomes (/DNA/genes) as the parent plant

Question 18

How can cancers grow?

Answer 18

The cell cycle goes out of control

Question 19

Describe what a ‘crown gall tumour‘ on a rose plant will look like?

Answer 19

A lump (often brown) on the stem

Question 19

Explain how crown gall tumours develop

Answer 19

There is a change to the cells that causes rapid and uncontrollable cell division

Question 20

What is the definition of growth?

Answer 20

An increase in size due to an increase in the number or size of cells

Question 21

What are percentile curves used for?

Answer 21

The graph shows the expected rate of growth of babies of different birth weights and is used to check that a child‘s growth is normal

Question 22

What are the three zones of growth in plants?

Answer 22

• zone of cell division (meristem)
• zone of elongation
• zone of differentiation

Question 23

Name the two types of stem cells in animals

Answer 23

Embryonic stem cells and adult stem cells

Question 24

Describe the differences between the two types of animal stem cells

Answer 24

Embryonic stem cells can produce any type of specialised cell whilst adult stem cells can only produce the type of specialised cell that is in the tissue around them

Question 25

Give three advantages of using stem cells to treat people

Answer 25

(1) no need to take anti-rejection drugs because cells are genetically identical (2) no need to find a donor (3) no need for tissue typing

Question 26

Give some disadvantages of using stem cells to treat people

Answer 26

(1) the stem cells may cause cancer if they continue to divide inside the body after they have replaced the damaged cells (2) cultured stem cells could be contaminated with viruses which would be transferred to a patient (3) no guarantees that the therapy will be successful (4) lack of stem cell donors (5) hard to obtain and store a person‘s embryonic stem cells - need to be collected near the start of the pregnancy

Question 27

What are the ethical problems of using stem cells to treat people or during research?

Answer 27

- one source of embryonic stem cells is unused embryos produced by ‘in vitro fertilisation‘ (IVF) - is it right to create embryos for therapy, and destroy them in the process? - embryos could come to be viewed as a commodity (item), and not as an embryo that could develop into a person - when should an embryo be regarded as, and treated as, a person?

Question 28

What are plant stem cells called?

Answer 28

Meristem cells

Question 29

Name two parts of a plant where stem cells can be found

Answer 29

- roots | - shoots

Question 30

What are chromatids?

Answer 30

The product produced when chromosomes replicate

Question 31

What cells is mitosis unlikely to occur in?

Answer 31

- sperm/egg cell (gametes) - red blood cell - lymphocyte

Question 32

Which structures of a flowering plant give rise to potatoes?

Answer 32

A potato is a tuber formed at the end of an underground stem

Question 33

Which structures of a flowering plant give rise to the fleshy scales of an onion?

Answer 33

Onion scales are modified leaves containing a food store

Question 34

In the process of tissue culture in plants, what is needed to induce the formation of a complete plant, in addition to a growth medium with nutrients?

Answer 34

The appropriate plant growth substances (‘hormones‘) would need to be added

Question 35

List four stimuli which can be detected by the skin

Answer 35

- heat - cold - touch - pressure

Question 36

How do we become aware of a stimulus?

Answer 36

Nerve impulses travel from a receptor to the brain

Question 37

Name the transparent outer layer found at the front of the eye

Answer 37

Cornea

Question 38

What is the retina?

Answer 38

It is the layer at the back of the eye that contains light receptor cells

Question 39

What is the pupil?

Answer 39

It is the hole in the centre of the eye through which light enters

Question 40

What is the iris?

Answer 40

The part of the eye that contains muscles that control the size of the hole in the centre of the eye

Question 41

Name the muscles that control the shape of the lens

Answer 41

Ciliary muscles

Question 42

Name the nerve that takes information from the eye to the brain

Answer 42

Optic nerve

Question 43

What happens to the optic nerve when a bright light shines in the eye?

Answer 43

Impulses travel in the optic nerve

Question 44

When a bright light shines in the eye, do the radial fibres in the iris contract?

Answer 44

No, the circular muscles in the iris contract to make the pupil smaller (in dim light the radial muscles contract to make the pupil larger)

Question 45

What responds when a bright light shines in the eye?

Answer 45

The retina

Question 46

What is the cause of the blind spot in the field of vision?

Answer 46

There are no sensory cells in the blind spot

Question 47

Which parts of the eye refract the light to form an image on the retina?

Answer 47

The curved surface of the cornea, and the lens

Question 48

What do you understand by the term ‘accommodation‘?

Answer 48

Accommodation is the way the eye can focus either near or distant objects to form a sharp image on the retina

Question 49

What part does the lens play in the the process of accommodation?

Answer 49

The lens is made thinner so that light from a distant object is refracted less, or fatter so that light from a close object is refracted more

Question 50

What happens to the ciliary muscle and lens for an eye to focus on a distant object?

Answer 50

The ciliary muscle relaxes and the lens gets thinner

Question 51

What happens to the ciliary muscle and lens for an eye to focus on a near object?

Answer 51

The ciliary muscle contracts and the lens gets thicker

Question 52

What is a cataract?

Answer 52

A cloudy patch on the lens

Question 53

Explain why cataracts cause blurred vision

Answer 53

Cataracts stop light from entering the eye as normal so less light reaches the retina

Question 54

What treatment is offered to people with cataracts?

Answer 54

The cataract lens can be surgically removed and is replaced by an artificial lens. Only one eye is done at a time so that the person can have vision

Question 55

What kind of eye defect can give rise to short-sightedness?

Answer 55

Long eyeballs, large eyeballs, too powerful a lens, or a combination of these defects

Question 56

What are the three names for the lenses that correct long-sightedness?

Answer 56

- converging (oval) - convex (oval) - meniscus (convex one side, concave the other side)

Question 57

Name the nerve fibres which carry impulses from the sense organs to the central nervous system

Answer 57

Sensory

Question 58

How can we tell which part of the body a sensory nerve impulse comes from?

Answer 58

Each part of the body is connected to its own region of the brain

Question 59

What is the function of an axon?

Answer 59

To carry the nerve impulse away from the cell body

Question 60

Describe the transmission of information from the stimulus of rods and cones in a dog‘s eye when it sees a cat, to the dog‘s muscles (via the CNS) as it responds and runs after the cat

Answer 60

Rods and cones (stimulus) —> sensory neurone/ optic nerve —> CNS (relay neurone) —> motor neurone —> muscle cells (response)

Question 61

What is a reflex?

Answer 61

A fast, automatic response to a stimulus (does not involve brain)

Question 62

Explain why neurones can deliver information very quickly

Answer 62

The signal is transmitted by electrical impulses

Question 63

Explain why doctors use electrical impulses to stimulate different parts of the brain

Answer 63

To find out what different parts of the brain do

Question 64

How do nerve impulses travel from one nerve to another?

Answer 64

The neurotransmitter is released by the axon of one neurone and diffuses across the gap to the dendrite of the other neurone. The neurotransmitter is absorbed into the dendrite which sets off an electrical impulse down the neurone.