Topic 2- Cells And Control

Question 1

What are chromosomes and the cell cycle?

Answer 1

Chromosomes- coiled up lengths of DNA molecules, which carry genes. They’re found in the nucleus and they’re normally in pairs in body cells.
Cells with two copies of each chromosome are diploid

Cell cycle- a series of stages in which cells divide to produce new cells.
When a cell is not dividing, it is in interphase.
Before dividing it does three things:
1. Grows in size
2. Increases the amount of sub cellular structures, E.g mitochondria and ribosomes
3. Duplicates it’s DNA

Question 2

What is mitosis?

Answer 2

Mitosis- the stages of the cell cycle when the cell divides
Prophase:
Chromosomes condense. Membrane around nucleus breaks down.
Metaphase:
Chromosomes line up the centre of cell.
Anaphase:
One set of chromatids pulled to each end of cell.
Telophase:
Nuclear membranes form around chromosomes.
Cytokinesis:
Cytoplasm and cell membranes divide resulting in two daughter cells are genetically identical to each other and to parent cell.

Question 3

What are the three methods of growth?

Answer 3

Plants and animals grow due to:
1. Cell differentiation- the process by which a cell changes to become specialised for its job.
2. Cell division- mitosis
3. Cell elongation- plants only

Question 4

What are Stem Cells?

Answer 4

Stem cells- undifferentiated cells that can divide to produce lots more stem cells, and can differentiate into many other types of cell.
Stem cells from adult animal can become many kinds of cell, E.g blood cells.
Human embryo can become any kind of human cell.
Plant meristem can become any kind of plant cell.

Question 5

What are benefits and risks of stem cells being grown in a lab?

Answer 5

Stem cells can be grown in a lab and made to differentiate.
Te specialised cells can transferred into people and so can be used in medicine:
Benefits:
Could replace cells that have been damaged by disease or injury, E.g new cardiac muscle cells could treat heart disease.
Risks:
Tumour development.
Disease transmission (if donor stem cells are infected with a virus).
Rejection by patients immune system.

Question 6

What does The Nervous System consist of?

Answer 6

Neurones- cells that carry information as electrical impulses in the nervous system.
The nervous system means that humans can react to their surrounding and coordinate their behaviour.
Central Nervous system- consists of the brain and spinal cord

Stimulus —> sensory receptor —> sensory neurone —> CNS —> motor neurone —> effector —> responses
Effectors can be muscles (which respond to nervous impulses by contracting) or glands (which secrete hormones

Question 7

What are the three types of Neurone?

Answer 7

1. Sensory Neurone- carries impulses from receptor cells to the CNS. consists of: receptor cells, dendron, axon and cell body
2. Motor Neurone- carries impulses from the CNS to effector cells. Consists of: cell body, myelin sheath, dendrites, axon and effector cells. Not all motor cells have myelin sheaths, sensory and relay can by myelinated too.
3. Relay Neurone- carries impulses from sensory neurones to motor neurones. Consists of: cell body, dendrites and axon
   The myelin sheath- acts as a pm insulator, speeding up the electrical impulse.

Question 8

What are synapses?

Answer 8

Synapse- the connection between two neurones.
A nerve signal is transferred across a synapse by the diffusion of neurotransmitters.
Electrical impulse travels to end of neurone where neurotransmitters are released.

Question 9

What are reflex arcs?

Answer 9

Reflexes- rapid, automatic responses to certain stimuli that don’t involve the conscious part of the brain. They can reduce the chance of injury.
Reflex arc- the passage of information in a reflex, from receptor to effector.
1. Stimulation of receptor.
2. Impulses travel along sensory neurone.
3. Impulses passed along relay neurone in CNS (spinal cord or unconscious part of the brain).
4. Impulses travel along motor neurone.
5. Effector responds, E.g muscle contracts.