Topic 2 - Cells and Control

Question 1

2.1 - What are the stages of the cell cycle?

Answer 1

Interphase - All the subcellular structures replicate
Prophase - Nucleus breaks down and spindle fibres appear
Metaphase - Chromosomes line up on the spindle fibres in the middle of the nucleus
Anaphase - Chromosome copies get separated on spindle fibres to opposite ends of the cell
Telophase - membrane forms around both sets of chromosomes forming two nuclei.
Cytokinesis - cell membrane forms around the two nuclei forming two identical daughter cells

Question 2

2.2 - What is the importance of mitosis in growth, repair and asexual reproduction?

Answer 2

Growth and repair - Multicellular organisms need new cells in order to grow and repair which is made through mitosis.
Asexual reproduction - Some organisms use this to produce clone offspring, this relies on mitosis.

Question 3

2.3 - Describe mitosis

Answer 3

Process where a diploid cell produces two genetically identical haploid daughter cells.

Question 4

2.4 - What is cancer?

Answer 4

Mutations in a cell leading to uncontrolled cell division

Question 5

2.5 - How do animals and plants grow?

Answer 5

Animals - Cells produced which don’t have a purpose can be specialised for a certain function, this is differentiation
Cell division increases number of cells and therefore increases growth ( increase in size or number of cells )

Plants - Meristems are groups of cells near the ends of shoots where cells rapidly divide, these cells then elongate in the zone of elongation, then the cells are differentiated into different specialised cells.

Question 6

2.6 - Explain the importance of cell differentiation

Answer 6

Each cell have certain features to be adapted to its function to carry out processes effectively.

Question 7

2.7 - How do percentile charts work?

Answer 7

a baby at 8 months and 6.8kg is on the 50th percentile.
50th percentile means 50% of babies have a mass less than 6.8kg.
These charts help show patterns in development.

Question 8

2.8 - What is the function of embryonic and normal stem cells in animals and plants?

Answer 8

Animal - Early stage embryo have stem cells that are able to differentiate into any specialised cell.As the cells continue dividing certain stem cells can only produce stem cells of the tissue around it.
Plants - produce any specialised cell in meristems and grow the plant.

Question 9

2.9 - What are the benefits and risks with stem cells in medicine?

Answer 9

Benefits - Bone marrow transplant treats type one diabetes and replaces damaged cells.
Risks - After stem cells replace damage cells they continue to divide causing cancer.
Also the stem cells from one person can be rejected by the person the cells are put into, this is rejection.

Question 10

2.10 - What are the structures and functions of the brain including cerebellum, cerebral hemispheres/cerebral cortex and medulla oblongata?

Answer 10

Cerebellum - controls balance, posture, timing and fine control
It is at the base of the brain.
Cerebral cortex - senses, language, memory, behaviour and feelings.
Left hemisphere communicates to right side and vice versa.
Medulla oblongata - reflexes like sneezing and heart rate.
Connects to neurones in spinal cord carrying information to brain and rest of body.

Question 11

2.11B - What difficulties are overcome to access brain tissue by using CT & PET scanning?

Answer 11

CT - X-ray beam moves around the head and measures different absorption from rays when the person thinks using different parts of the brain. No surgery required.
PET - Patient injected with radioactive glucose, more active cells take in more glucose so gamma rays are higher in areas of high glucose. Doesn’t damage the brain.

Question 12

2.12B - What are the limitations of treating disease in brain and nervous damage?

Answer 12

Nerve damage - can’t be fixed as stem cells can’t differentiate into neurones so can’t repair. Although

Question 12

2.12B - What are the limitations of treating disease in brain and nervous damage?

Answer 12

Nerve damage - can’t be fixed as stem cells can’t differentiate into neurones so can’t repair. Although electrical wires can be used to stimulate nerve impulses the patient doesn’t regain feeling of movement.
Brain damage - Cancer tumours can be killed using radiotherapy ( gamma rays killing tumour ) and chemotherapy ( injecting drugs to kill tumour ). But chemotherapy may not work due to blood brain barrier.

Question 13

2.13 - What is the structure and function of sensory receptors, sensory , relay and motor neurones and synapses, axon, dendron, myelin sheath and
neurotransmitters?

Answer 13

Sensory receptors - These detect the changes in the environment (stimulus)
Sensory neurones - Nerve cells that send a signal from the sensory receptors to the CNS
Relay neurones - carry nerve impulses within the central nervous system
Motor neurones - carry nerve impulses away from the central nervous system.
Synapses - Where neurones meet, there is a small gap called a synapse
Axon - stimulates the second neuron to transmit an electrical impulse along its axon
Dendron - carry electrical impulses from one place to another
Myelin sheath - fatty layer that surrounds the axon. The sheath acts as an insulator and speeds up nerve impulses.
Neurotransmitters - stimulates the second neuron to transmit an electrical impulse along its axon

Question 14

2.14 - Describe a reflex arc

Answer 14

A receptor in the skin detects a stimulus (the change in temperature).
Sensory neurones send electrical impulses to relay neurones, which are located in the spinal cord. They connect sensory neurones to motor neurones.
Motor neurones send electrical impulses to an effector.
The effector produces a response (muscle contracts to move hand away).

Question 15

2.15B - What is the structure and function of the eye?

Answer 15

Cornea - Refracts light bends it as it enters the eye
Lens - Further refracts light to focus it onto the retina
Iris - Controls how much light enters the pupil
Rod - sensitive to light to see in dim light.
Cone - not sensitive to light and react at higher light levels and sensitive to colours.

Question 16

2.16B - Describe defects of the eye

Answer 16

Cataract - A cataract is a cloudiness in the lens, caused by a build up of protein inside the lens.
Long sightedness - Someone who is long-sighted can see distant objects clearly, but they cannot focus properly on near objects.
Short sightedness - Someone who is short-sighted can see near objects clearly, but cannot focus properly on distant objects.
Colour blindness - one cone cell type doesn’t function properly. This means that people with colour vision deficiency cannot see the full visible spectrum, and instead see many colours the same.

Question 17

2.17B - How can cataracts, long sightedness and short sightedness can be corrected?

Answer 17

Short-sightedness can be corrected by placing a concave lens in front of the eye,
Long-sightedness is corrected by putting a convex lens in front of the eye
Laser surgery – reshapes the cornea surgically. Common for myopia but can be used for some hyperopia conditions.
Replacement lens – implanting artificial lenses is a recent development, and can placed in front of the original lens, through a small cut in the cornea, to correct an eye defect.