Topic 2 - Cells And Control

Question 1

What is mitosis?

Answer 1

Mitosis is a type of cell division in which a diploid body cell copies itself and finally divides into two identical daughter cells.
The daughter cells are clones of each other, their DNA is identical.

Question 2

What is mitosis used for?

Answer 2

Growth, repair and asexual reproduction.

Question 3

What are the stages of the cell cycle?

Answer 3

Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

Question 4

What happens in the interphase?

Answer 4

• New sub-cellular structures made e.g. mitochondria
• DNA replicates

Question 5

What happens in the prophase?

Answer 5

• DNA unwinds and condense into chromosomes
• Nucleus membrane breaks down
• Spindle fibres become visible

Question 6

What happens in the metaphase?

Answer 6

• The spindle fibres attach to the chromates at the centromere
• The chromates line up along the equator/centre of the cell

Question 7

What happens in the anaphase?

Answer 7

• The spindle fibres shorten and pull the chromates apart to the poles of the cell (each chromosome is identical to its copy)

Question 8

What happens in the telophase?

Answer 8

A nuclear membrane forms around each set of chromosomes, separating them to form two new nuclei.

Question 9

What happens in cytokinesis?

Answer 9

Cytoplasm splits to create 2 separate genetically identical diploid cells.

Question 10

What are stem cells?

Answer 10

Stem cells are cells that can turn into different types of cell - they are undifferentiated (not specialised).
Stem cells can divide to make more stem cells or they can differentiate.
Once differentiated, a cell can’t turn into another type of cell.

Question 11

What is an embryonic stem cell?

Answer 11

Embryonic stem cells can become almost any cell type in the body, they are unspecialised. Can only be found in the embryo stage of development.

Question 12

What is an adult stem cell?
One function of adult stem cells

Answer 12

Adult stem cells are found only in certain places in the body with differentiated tissues e.g. bone marrow. They can only become a limited range of cell types (multipotent).

Function: To replace damaged cells, e.g. make new skin or blood cells.

Question 13

What is the meristem?

Answer 13

Cell division in plants occurs in regions called the meristem. They are found in areas where the plant is growing e.g. roots. Meristems produce pluripotent cells that can produce any plant cell. They are undifferentiated and they divide to produce more differentiated cells by mitosis.

Question 14

Benefits and drawbacks of embryonic stem cells?

Answer 14

+ Easy to remove from embryo
+ Pluripotent - could treat a vast number of diseases
+ Could be cloned from patients own cells to avoid rejection
- Ethical issues with destroying embryos to get stem cells (i.e. murder in the opinion of Catholics)
- Could lead to illegal cloning of humans

Question 15

Risks of embryonic stem cells?

Answer 15

• Risk of rejection if the stem cells from another person
• Risk of infection
• Risk of tumours - if unable to control rate at which transplanted cells divide

Question 16

Adult stem cells benefits and drawbacks?

Answer 16

+ If taken from the person being treated then no rejection.
+ No ethical issues
- Difficult to identify and remove from tissues in the body (mixed up with differentiated cells)
- Multipotent can only treat a limited range of diseases

Question 17

Adult stem cells risks?

Answer 17

• Differentiated cells may be rejected when used in treatment as cells come from a different person
• Risk of infection
• Risk of tumours - if unable to control rate at which transplanted cells divide

Question 18

How can we measure growth?

Answer 18

• Size - The height, length, circumference and width can be measured.
• Wet mass - Includes all the mass in an organism in its body. (This is highly variable/can fluctuate)
• Dry mass - Mass of an organism which has no water present (organism must be dead).

Question 19

What 3 things need to happen for growth to happen in a plant?

Answer 19

1) Cell division - mitosis
2) Cell elongation - takes place in plant cells only where the plant expands making the cell bigger.
3) Cell differentiation - stem cells are able to change to become various types of specialised cells.

Question 20

What has to happen for growth in animals?

Answer 20

1) Cell division - mitosis
2) Cell differentiation

Question 21

What does it mean to be in the 95th percentile for a heigh of 175cm?

Answer 21

95% of people are shorter and 5% of people are taller of that age.

Question 22

Why do animals have a nervous system?

Answer 22

Allows you to detect and respond to stimuli. Enables you to control your body.

Question 23

What 2 parts is the nervous system made up of?

Answer 23

• CNS - Central nervous system
• PNS - Peripheral nervous system

Question 24

Central nervous system

Answer 24

Made of:
• Brain
• Spinal cord
The CNS co-ordinates responses to a stimulus (e.g. tells the body what to do if a change is detected)

Question 25

Peripheral nervous system

Answer 25

The rest of the nervous system connects the sense organs to the CNS using neurones e.g. skin, eyes.

Question 26

How is information through sent through the nervous system?

Answer 26

As electrical impulses - these are electrical signals that pass along nerve cells known as neurones. A bundle of neurones is known as a nerve.

Question 27

What is the co-ordination pathway in the nervous system?

Answer 27

Sensory receptors are groups of cells that detect a stimulus (a change in the environment e.g. light receptors in your eyes, touch receptors in your skin.) This information is converted into and electrical impulse and sent to the CNS, where a response is coordinated, and information is sent to an effector e.g. a muscle or gland. Stimulus Receptor CNS Effector Response

Question 28

Motor neuron

Answer 28

Transmits electrical impulses from the relay neurone to the effector e.g. muscle. Long and have a large cell body at one end with long dendrites branching off.

Question 29

Sensory neuron

Answer 29

Transmits electrical impulses from receptors to the relay neurone. Long and have a cell body branching off the middle of the axon.

Question 30

Relay neurones

Answer 30

Transmits electrical impulses from the sensory neurone to the motor neurone. Short and have a small cell body at one end with many dendrites branching off it.

Question 31

What do all the neurones have in common?

Answer 31

They transmit electrical impulses.

Question 32

Stages of Neurotransmission

Answer 32

1) Electrical impulse reaches axon terminal. 2) Neurotransmitters diffuse across the synapse. 3) Electrical impulse is generated at the dendrite. 4) The electrical impulse travels down the next neuron.

Question 33

Synapse

Answer 33

A gap between to neurones.

Question 34

Myelin sheath

Answer 34

Insulates the axon and speeds up the impulse.

Question 35

Dendrites

Answer 35

Many extensions called dendrites extend out from the cell body of the neurone and at the far end of the axon. This means neurones can connect to many other neurones and receive impulses from them, forming a network for easy communication.

Question 36

Cell body

Answer 36

Where the nucleus and main organelles are found and cytoplasmic extensions from this body called axons and dendrites.

Question 37

How do strong painkillers work?

Answer 37

Strong painkillers prevent neurotransmitters binding to receptors in the next neurone. Therefore an electrical impulse is not triggered and a signal is not received by the CNS so the person doesn’t feel pain.

Question 38

Why are reflexes important?

Answer 38

When you need to react fast your body doesn’t have time to send the signal to the brain and so only sends the signal to the spinal cord. This is the reflex arc, which involuntary.

Question 39

Name the main process by which plants grow in height?

Answer 39

Cell elongation

Question 40

Differences between the growth of animals and growth of plants?

Answer 40

1) All growth in animals happens by cell division but growth in plants happens by cell elongation and cell division 2) Animals grow while they are young and stop growing while plants grow continuously.

Question 41

How does a tumour form?

Answer 41

A change in one of the genes that controls cell division causes cells to divide uncontrollably which creates an abnormal mass of cells (tumour).

Question 42

What point is a tumour classified as cancer?

Answer 42

When the tumour invades and destroys surrounding tissues.

Question 43

2 structural differences between a motor neurone and a sensory neurone?

Answer 43

1) The sensory neurones cell body branches of the middle of the axon where as motor neurones have a cell body at one end. 2) Sensory neurones have a short axon where as motor neurones have a long axon.

Question 44

Stages of the reflex arc (Not detailed)

Answer 44

Stiumulus Receptor Sensory neurone Synapse Relay neurone Synapse Motor neurone Effector Response

Question 45

Stages of the reflex arc (Detailed)

Answer 45

1) A stimulus is a change in the environment of an organism. 2) This is detected by a receptor such as the eye. 3) Impulses from the receptor pass along a sensory neurone to the central nervous system. 4) A chemical crosses the gap (synapse) between a sensory neurone and a relay neurone in the spine. 5) Then a chemical crosses the synapse between a relay neurone and a motor neurone. 6) The motor neurone carries an impulse to an effector which can be a muscle or gland. 7) A muscle responds by contracting, a gland responds by releasing chemical substances.

Question 46

How is a signal transmitted at a synapse?

Answer 46

Neurones transmit electrical impulses which trigger the release of neurotransmitters. These diffuse across a synapse as a chemical signal. Neurotransmitters bind to receptors on the next neurone triggering an electrical impulse in the next neurone.