B2 - Cells and Control

name the stages of the cell cycle and their functions

1. Interphase - the cell grows and duplicates sub-cellular structures

2. Prophase - chromosomes condense (untangle), nuclear membrane disintegrates, spindle fibres form

3. Metaphase - chromosomes line up along the centre of the cell

4. Anaphase - chromosomes split into 2 chromatids and are pulled to opposite poles of the cell

5. Telophase - new nuclear membranes form

6. Cytokinesis - the cytoplasm divides

Mitosis - which cells? for what? daughter cells?

Used by body cells.

Repair, growth and asexual reproduction.

2 diploid, genetically identical, daughter cells

Cancer

A mutation in a gene that controls cell division that leads to uncontrollable cell division and sometimes a tumour which invades and destroys surrounding tissue

How does growth happen in animals?

All growth happens by cell division. When younger, cells divide at a faster rate but when an adult, most of the division is for repair to replace old or damaged cells. Cell differentiation is lost at an early age

How does growth happen in plants?

Growth in height is mainly due to elongation. Cell division happens in the meristem areas (shoots and roots). But plants grow continuously throughout their lives.

How to monitor growth in children?

Use a percentile chart to see overall pattern in development. Take measurements of length, mass and head circumference. Chart shows percentiles (e.g. 50th percentile shows the mass that 50% of babies will have reached at that age)

Where are stem cells found in humans and why are they useful?

Found in early human embryos and bone marrow. Have the potential to divide and produce any kind of cell. Important for growth and development. Adult stem cells are used to replace damages cells but they are not as versatile as embryonic stem cells

Where are stem cells found in plants and why are they important?

Found in the meristem areas (the areas that can divide - roots and shoots). Can divide and differentiation for as long as the plant lives.

How are stem cells being used in medicine?

Adult stem cells are already used to cure some diseases e.g. bone marrow transplant. Scientists are experimenting with extracting embryonic stem cells from early embryos which, under certain conditions, can be stimulated to specialise. These can be used to replace cells that have been damaged by disease or injury.

What are the drawbacks of stem cells in medical use?

1. Tumour development - unable to control the rate of division of the stem cells

2. Disease transmission - if donor cells are infected with a virus it could be passed on

3. Rejection - may be detected as foreign and trigger an immune response

4. Ethical issues - some thinks that an embryo is a human life and so should not be extracted and used for medicine

State and describe the functions of the areas of the brain

• Cerebrum - largest part, divided into two cerebral hemispheres (right controls left muscles etc.), responsible for movement, intelligence, memory, language and vision

• Cerebellum - responsible for muscle coordination and balance

• Medulla oblongata - responsible for unconscious activities such as breathing and heart rate

CT scan vs PET scan

PET shows both structure and function whilst CT only shows structure.

PET uses radioactive chemicals whilst CT uses X-rays.

Dangers of treating problems in the central nervous system

1. Hard to repair damage to the nervous system - scientists cannot repair nervous tissue

2. Hard to access certain parts (e.g. not possible to remove tumours from certain parts of the brain)

3. May lead to permanent damage - e.g. surgery on spinal chord could lead to further damage such as paralysis

Describe the route of a stimulus to a response

Stimulus - receptor - sensory neurone - CNS (relay neurone) - motor neurone - effector - response

Describe the structure of a sensory neurone

One long dendron carries nerve impulses from receptor cell to the cell body. One short axon carries the impulse from the cell body to the CNS

Describe the structure of the motor neurone

Many short dendrites carry nerve impulses from the CNS to the cell body. One long axon carries the impulse from the cell body to effector cells

Describe the structure of the relay neurone

Many short dendrites carry nerve impulses from sensory neurones to the cell body. An axon carries the impulses from the cell body to motor neurones

What connects neurones and how do they work?

Neurones are connected by synapses. Neurotransmitters triggered by the electrical impulse diffuse across the synapse and trigger a new electrical signal in the next neurone

Describe the reflex arc

1. Stimulus is detected by receptor cells and an impulse is sent along a sensory neurone

2. When it reaches the synapse between the sensory and relay neurone, it triggers neurotransmitters to be released which carry impulses to be sent along the relay neurone.

3. Same thing happens at the synapse between relay and motor neurone

4. Impulse travels along the motor neurone to the effector which triggers a response

Describe the functions of the different parts of the eye including:

• Cornea

• Iris

• Lens

• Retina

• Rods

• Cones

• Optic nerve

• Cornea - refracts light into the eye

• Iris - controls how much light enters the pupil

• Lens - refracts light, focusing it onto the retina

• Retina - light sensitive, covered in rods and cones which detect light

• Rods - detect dim light

• Cones - detect colour

• Optic nerve - carries electrical impulses from eye to brain

How does the eye focus on

1. Near

2. Far

objects?

1. Ciliary muscles relax and suspensory ligaments contract so less round and refracted less

2. Ciliary muscles contract and suspensory ligaments relax so eye is more round and more refraction of light

Describe long and short sightedness and how they can be corrected

Long - lens doesn’t bend the light enough, eye is too short. Light focused beyond retina. Fixed with a convex lens

Short - lens bends the light too much or eye is too long. Light focused before retina. Fixed with concave lens

What are colour blindness and cataracts and how can they be solved?

Colour blindness - red/green is when the red and green cones in the retina are not working properly and it cannot be cured as the cones cannot be replaced.

Cataracts - a cloudy patch on the lens stopping light entering the eye normally resulting in blurred vision, can be treated by replacing the faulty lens with an artificial one.