SB2 - Cells and Control

Question 1

What is the cell cycle?

Answer 1

The cell cycle is the process by which an organism creates new cells, it has two phases, interphase and mitosis.

Question 2

What happens in interphase?

Answer 2

In interphase, the organelles and DNA are replicated and normal cell function continues.

Question 3

What happens in prophase?

Answer 3

In prophase, the nuclear membrane breaks down and the spindle fibres grow. The chromosomes also condense.

Question 4

What happens in metaphase?

Answer 4

In metaphase, the chromosomes line up in the centre of the cell and the spindle fibres attach to the centromeres of the chromosomes.

Question 5

What happens in anaphase?

Answer 5

In anaphase, the chromatids are pulled to opposite poles of the cell.

Question 6

What happens in telophase?

Answer 6

In telophase, a membrane forms around the chromatids to form nuclei.

Question 7

What happens in cytokinesis?

Answer 7

In cytokinesis, the cytoplasm splits and a cell surface membrane forms to separate the two cells. Cell walls also form in plant cells.

Question 8

What causes the growth of tumours?

Answer 8

Sometimes, mutations in DNA cause the cell to begin dividing when it shouldn’t (uncontrolled mitosis), forming a tumour.

Question 9

What is growth?

Answer 9

Growth is an increase in size as a result of an increase in number of or size of cells.

Question 10

Why are percentiles growth charts used?

Answer 10

They are used to check the growth and development of a baby, to make sure that they are growing normally and there aren’t any health issues.

Question 11

What things are measured on percentiles growth charts?

Answer 11

Mass, length, head circumference

Question 12

What does it mean if a baby is in the 25th percentile for mass?

Answer 12

It means that 25% of babies are lighter than them (also 75% are heavier).

Question 13

What is differentiation?

Answer 13

Differentiation is the process by which unspecialised cells become specialised for a particular function.

Question 14

What are meristems?

Answer 14

Meristems are parts of a plant found at the shoot tip and root tip which contain stem cells. They divide rapidly by mitosis and allow the plant to continue growing throughout its life.

Question 15

What is elongation?

Answer 15

Elongation is one way in which plants grow. The links between cellulose molecules are loosened, allowing water to enter the cell causing the expansion of the vacuole and cytoplasm, the links reform between cellulose molecules and the cell wall becomes rigid again.

Question 16

Evaluate the use of embryonic stem cells to treat human diseases.

Answer 16

S - embryonic stem cells are pluripotent (can become any type of specialised cell), less chance of rejection
W - ethical issues as embryo is killed when stem cells are extracted, procedure needs more testing to evaluate its safety, could transfer viral infections, chance of rejection

Question 17

Evaluate the use of adult stem cells to treat human diseases.

Answer 17

S - donor is able to consent to giving stem cells, procedure is safe
W - higher chance of rejection, adult stem cells are multipotent (can only differentiate into some types of cell), chance of transferring viral infections

Question 18

What is therapeutic cloning?

Answer 18

When an egg cell from a donor has its nucleus removed and a cell from the patient has its nucleus removed and placed in the egg cell. This stimulates the growth of an embryo and after 4-5 days the stem cells are removed and cultured for therapeutic use. This lowers chances of rejection as the cells contain DNA from the patient.

Question 19

Describe the cerebral cortex.

Answer 19

The cerebral cortex takes up about 80% of the brain. It is divided into two hemispheres, each with different functions. The right hemisphere communicates with the left side of the body and vice versa. Used for senses, language, memory, behaviour, consciousness and controls voluntary responses. It is wrinkled, which increases its surface area, which increases its capacity for complex functioning.

Question 20

Describe the cerebellum.

Answer 20

The cerebellum is located at the base of the brain. It is divided into two halves and controls unconscious functions such as balance, posture and it coordinates fine motor control.

Question 21

Describe the medulla oblongata.

Answer 21

The medulla oblongata regulates functions such as heartbeat, blood pressure, breathing rate and controls reflexes such as vomiting, swallowing, coughing and sneezing. It connects the brain to the spinal cord.

Question 22

How can the brain be investigated through surgery?

Answer 22

Brain surgery - electrodes can be used to stimulate parts of the brain and patients may be asked to describe what they feel or may make patients do something or stop an action from occurring. This allows the functions of the brain to be investigated.

Question 23

How can brain functions be investigated through scans?

Answer 23

PET scan - patient is injected with radioactive glucose. More active cells take in more glucose than less active cells for respiration. The radioactive atoms cause gamma rays, which the scanner detects. Carrying out activities during a PET scan causes specific areas of the brain to be more active. PET scans can also be used to diagnose and track cancer (as it shows which cells are dividing most).

Question 24

How can CT scans be used to diagnose a brain tumour?

Answer 24

In a CT scan, an X-ray beam moves in a circle around the head and detectors measure the absorption of the X-rays. A computer uses this information to build up a view of the body as a series of ‘slices’. Tumours show up on CT scans as white blotches. This can also investigate brain function, as it shows the structures of the brain, which can be linked to differences in the way people think and act, suggesting what certain parts do.

Question 25

How can brain tumours be treated?

Answer 25

Surgery - they can be cut out Radiotherapy - cancer cells killed by high energy X-ray beams Chemotherapy - injecting drugs which kill actively dividing cells (although this may not be effective due to the blood-brain barrier, a natural filter which only allows certain substances from the blood to get into the brain).

Question 26

Describe the effects and treatments of spinal cord damage.

Answer 26

Damage to the spinal cord reduces the flow of information between the brain and parts of the body. Nerve damage in the lower spinal cord can cause loss of feeling in the legs. Damage in the neck can cause quadriplegia (loss of use of both arms and legs). Wires can be used to electrically stimulate nerves and muscles below the damage, but patients do not regain full movement or feeling. However, treatments using stem cell injections are being developed.

Question 27

What is the CNS?

Answer 27

The CNS (central nervous system) is an organ system made up of the brain and spinal cord. It allows all parts of the body to communicate, using electrical impulses.

Question 28

How does the CNS produce a response to stimuli?

Answer 28

Receptor cells detect the stimulus and create impulses, which travel to the brain. The information is processed in the brain and sends impulses to an effector, where a response is generated.

Question 29

Describe the structure of a sensory neurone and their functions.

Answer 29

Sensory neurones carry electrical impulses from the receptors to the CNS. The impulse will first reach the dendrites, where it is then transmitted along the dendron, then the axon. The axon terminals allow impulses to be transmitted to other neurones. The axon and dendron are long, to allow for faster transmission. There is also a layer surrounding the neurone called myelin sheath, which insulated the impulse and makes it travel faster.

Question 30

Describe a motor neurone and its function.

Answer 30

Motor neurones carry electrical impulses from the CNS to an effector. The impulse first reaches the dendrites, then axon, then the axon terminals. In motor neurones, there is no dendron and the axon is long. Myelin sheath are along the axon and insulate the impulse.

Question 31

Describe a relay neurone and its function.

Answer 31

Relay neurones transmit impulses within the CNS. They are much smaller than motor and sensory neurones. The impulse first reaches the dendrites, then the axon, then axon terminals.

Question 32

Describe what happens at a synapse.

Answer 32

Synapses are gaps between neurones. When an impulse reaches an axon terminal, neurotransmitter is released which diffuses across the synaptic gap, The receptors on the next neurone detect the neurotransmitter and generate a new electrical impulse.

Question 33

Why do we need synapses?

Answer 33

Synapses slow down neurotransmission, however we need them because they ensure that the electrical impulse will only flow in one direction (as neurotransmitter is only released from the axon terminals).

Question 34

What is the reflex arc?

Answer 34

The reflex arc describes the pathway electrical impulses take when a reflex reaction takes place (e.g. dropping a hot object). The receptors detect the stimulus and an electrical impulse is generated,which passes along sensory neurones to the spinal cord where it is relayed to the motor neurones, which it passes along until it reaches an effector and a response is generated. The reflex arc bypasses the parts of the brain involved in processing information and so generate quicker responses needed to prevent injury.

Question 35

What is the retina?

Answer 35

The retina is found at the back of the eye and contains rod and cone cells, which detect light intensity and colour.

Question 36

What are rod cells?

Answer 36

Rod cells are a type of receptor cell which detect light intensity - they are found in the retina, they work well in bright light and dim light.

Question 37

What are cone cells?

Answer 37

Cone cells are a type of receptor cell which detect light colour - they are found in the retina, they work best in bright light.

Question 38

What is the pupil?

Answer 38

The pupil is the dark circle in the middle of the eye, it lets light into the eye.

Question 39

What is the iris?

Answer 39

The iris is the coloured part of the eye, it can constrict and dilate to allow more or less light onto the retina.

Question 40

What is the cornea?

Answer 40

The cornea is a clear, curved covering which focuses light on to the retina.

Question 41

What is the lens and ciliary muscles?

Answer 41

The lens is used to fine-tune the focusing, the ciliary muscles change the shape of the lens so that it can focus on near or far objects.

Question 42

What is the optic nerve?

Answer 42

The optic nerve contains bundles of neurones which connect the eye to the brain.

Question 43

What is short-sightedness and how can it be treated?

Answer 43

Short-sightedness is caused by either the eyeball being too long or the cornea being too curved. It is when light focuses in front of the retina, so the image you see is blurry. It can corrected using glasses fitted with a diverging lens.

Question 44

What is long-sightedness and how can it be treated?

Answer 44

Long-sightedness is caused by either the eyeball being too short or the cornea not being curved enough. It is when light focuses behind the retina, so the image you see is blurry. It can be corrected using glasses fitted with a converging lens.

Question 45

What is cataracts and how can it be treated?

Answer 45

Cataracts is caused by a build up of protein inside the lens, which makes it cloudy. This can be treated by surgically replacing the damaged lens with a plastic one.

Question 46

What is colourblindness?

Answer 46

Colour-blindness is when some of the cone cells are faulty, so the person has trouble seeing colour. The most common form is red-green colourblindness, in which the green cones do not work. Colour-blindness cannot be corrected.