Topic 2 - Cells and Control

Question 1

Describe mitosis

Answer 1

Mitosis is a step in the cell cycle that cells must undergo in order to divide. Mitosis is the stage where the cell divides.

It’s the process that involves a cell dividing to produce 2 identical cells.

Question 2

Describe interphase

Answer 2

In this stage the cell grows, organelles (such as ribosome and mitochondria) grow and increase in number, the synthesis of proteins occurs, DNA is replicated and the energy stores are increased.

Question 3

Describe prophase

Answer 3

The DNA in chromosomes and their copies condenses to become more visible. The membrane around the nucleus breaks down.

Question 4

Describe metaphase

Answer 4

Chromosomes and their copies line up in the middle of the cell

Question 5

Describe anaphase

Answer 5

Spindle fibres split the chromosomes down the centre and pull one chromatid to either side of the cell.

Question 6

Describe telophase

Answer 6

New membranes form around the chromosomes at either end of the cell

Question 7

Describe cytokinesis

Answer 7

The cell cytoplasm and membrane divides to produce two daughter cells; each new cell has a copy of each of the chromosomes.

Question 8

Describe the importance of mitosis

Answer 8

It’s important in growth, repair and asexual reproduction.

Question 9

Describe the division of a cell by mitosis

Answer 9

It is the production of two daughter cells, each with identical sets of chromosomes in the nucleus to the parent cell, which results in the formation of two genetically identical diploid body cells

Question 10

Describe cancer

Answer 10

The result of changes in cells that lead to uncontrolled cell division

Question 11

Describe growth in animals (highlighting cell division and differentiation)

Answer 11

In animals, cell division occurs by mitosis, after which cells can differentiate to specialised forms, specially adapted to their function.

Question 12

Describe growth in plants (highlighting cell division, elongation and differentiation)

Answer 12

Plant cells can grow longer in a specific direction by absorbing water into their vacuoles, and this is controlled by substances called auxins. Mitosis only occurs in meristems in the tips and roots and shoots in plants.

Question 13

Explain the importance of cell differentiation in the development of specialised cells (?? remove)

Answer 13

In animals, almost all cells differentiate at an early stage and then lose this ability. Most specialised cells can make more of the same cell by undergoing mitosis.
In plants, many types of cells retain their ability to differentiate through life.

Question 14

Describe what a baby being born at the 50th percentile for mass means

Answer 14

The baby Is heavier than 50% of babies.

Being in a high percentile can indicate a health problem.

Question 15

Describe the function of embryonic stem cells

Answer 15

-They can differentiate into any type of cell in the body.

-They form when an egg and sperm cell fuse to form a zygote.
-Scientists can close the cells and direct them to differentiate into almost any cell in the body

Question 16

Describe the function of stem cells in animals

Answer 16

Adult stem cells can differentiate into related cell types only. So bone marrow cells can differentiate into blood cells and cells of the
immune system, but not other cell types.

Question 17

Describe the function of meristems in plants

Answer 17

-They can differentiate into any type of plant, and have this ability throughout the life of the plant

-Found in root and shoot tips
-Can be used to make clones of the plant - this may be necessary if the parent plant has certain desirable features, for research or to save a rare plant from extinction.

Question 18

Discuss the potential benefits associated with the use of stem cells in medicine

Answer 18

-Can be used to replace damaged or diseased body parts
-Unwanted embryos from fertility clinics could be used as they would otherwise be discarded.
-Potential for medical research into the process of differentiation.
-Potential for treating patients with currently untreatable conditions
-Potential for growing organs for transplants

Question 19

Discuss the potential risks associated with the use of stem cells in medicine

Answer 19

-There is no guarantee of how successful these therapies will be, for example in the use of stem cells in healing damage caused by Parkinson’s disease.
-Patients could be exploited by paying for expensive treatments and being given false hope of a cure as stem cell therapies are only in their developmental stages.
-The difficulty in finding suitable stem cell donors.
-The difficulty in obtaining and storing a patient’s embryonic stem cells.
-Cultured stem cells could be contaminated with viruses which would be transferred to a patient.
-People may have religious or ethical objections as it is seen as interference with the natural process of reproduction

Question 20

Describe the structures and functions of the cerebellum

Answer 20

Large lump-like structure at the bottom of the brain, on the rear side.
It is responsible for controlling minor movements and balance.

Question 21

Describe the structures and functions of the cerebral hemisphere

Answer 21

The two large cerebral hemispheres (together the cerebral cortex or cerebrum) take up most of the skull and perform a variety of functions including for memory, intelligence, language, conscious thought, voluntary movement.

The left hemisphere of the brain controls the right side of the body and vice versa.

Question 22

Describe the structures and functions of the medulla oblongata

Answer 22

It is a small elongated structure found in the brainstem, at the base of the brain. It is responsible for involuntary actions such as the heartbeat and breathing.

Question 23

Explain how the difficulties of accessing brain tissue inside the skull can be overcome by using CT scanning

Answer 23

CT scans use x-ray radiation from several angles to generate a 3D image of the brain. This is useful for examining bleeding within the skull and damage to brain structures.

Question 24

Explain how the difficulties of accessing brain tissue inside the skull can be overcome by using PET scanning

Answer 24

In PET scans, radioactive glucose / a ‘tracer’ is injected into the blood before the scan. The scan itself shows the area where the tracer builds up to show area with greater blood flow. This can identify cancerous tumours as these use more blood than normal tissue.

Question 25

Explain some of the limitations in treating damage and disease in the brain and other parts of the nervous system, including spinal injuries and brain tumours

Answer 25

-It is complex and delicate
-It is easily damaged
-Drugs given to treat diseases cannot always reach the brain because of the membranes that surround it
-It is not fully understood which part of the brain does what
-Often, tumours can be buried deep in the brain or spinal cord, making them especially difficult to remove.

Question 26

Explain the structure and function of a reflex arc

Answer 26

-Sensory receptors on sensory organs detect a stimulus and convert it into an electrical impulse.
-This electrical impulse travels along nerve cells called sensory neurones to the central nervous system where the impulse passes to a relay neurone.
-The impulses are then sent along to a motor neurone.
-It then moves to the effector which carries out an appropriate response.

Question 27

What are some features of a neurone?

Answer 27

-A long fibre (axon) which is insulated by a fatty (myelin) sheath. They are long so they can carry messages up and down the body.
-Tiny branches (dendrons) which branch further as dendrites at each end. These receive incoming impulses from other neurones.

Question 28

Describe what happens at synapses.

Answer 28

Synapses are the gaps between two neurones. They control the speed of the impulse.

At the end of an axon of the first nerve cell, a chemical called a neurotransmitter is released into the synapse. This diffuses across the synapse and carries the signal to receptors on the other nerve cell. The receptor generates an electrical impulse that carries on along the nerve cell.

Question 29

Explain the role of the cornea

Answer 29

Focuses light, is in a fixed shape

Question 30

Explain the role of the lens

Answer 30

Focuses light, can change shape to refract light

Question 31

Explain the role of the iris

Answer 31

Coloured part of the eye

Question 32

Explain the role of the rod cells in the retina

Answer 32

Receptor cells that detect light intensity

Question 33

Explain the role of the cone cells in the retina

Answer 33

Receptor cells that detect colour

Question 34

Describe short-sightedness

Answer 34

Short-sightedness is also called myopia and is when light rays are too focused in front of the retina and the cornea refracts light rays too much. The cornea is too convex.

Question 35

Describe long-sightedness

Answer 35

Long-sightedness is also called hyperopia and is when light rays are too focused behind the retina and the lens doesn’t refract light enough. The eyeball is too short.

Question 36

Describe cataracts

Answer 36

A build-up of protein in the lens, causing it become cloudy. It restricts vision

Question 37

Describe colour blindness

Answer 37

The inability to see certain colours. This usually occurs because people with the condition do not have enough cone cells in their retina. This is usually genetic.

Question 38

Explain how cataracts, long-sightedness and short-sightedness can be corrected

Answer 38

*With spectacle lenses/contact lenses -concave lenses to focus the light on the fovea for short-sightedness and convex lenses to bring the rays together to treat hyperopia
*For cataracts, the lens can be replaced with a plastic one