CB2 - Cells and Control

Asexual reproduction

Where an organism created genetically identical couples of itself, often by mitosis.

Sexual reproduction

Where an organism created genetically different versions of itself, involving two parents and fertilisation of gametes.

Structure of DNA

Double helix shape.

Each strand has a sugar-phosphate backbone.

Contains complimentary bases, joined by hydrogen.

Complimentary base pairs

A with T

C with G

Genome

All the genetic information in an organism

Gene

A section of DNA that codes for a specific protein - can be 1000s of based long.

How to extract DNA from plant cells?

Grind up cellular tissue

Add salt (to disrupt the membranes)

Add detergent (to dissolve the membranes)

Heat and filter, collect filtrate

Add ice cold ethanol to precipitate the DNA - white strings

Two stages of the cell cycle

Interphase and mitosis

What happens in interphase?

Normal cell processes, then new sub-cellular parts are made, chromosomes are copied for mitosis.

Stages of mitosis in order

Prophase, metaphase, anaphase, telophase, cytokinesis

Prophase

Nucleus breaks down, spindle fibres appear.

Metaphase

Chromosomes line up on equator of cell

Anaphase

Chromosomes copies are pulled apart to opposite poles by the spindle fibres.

Telophase

New nuclei form around split chromosomes.

Cytokinesis

Cell membrane separates into 2 cells.

Cells produced by mitosis

Two genetically identical, diploid daughter cells.

Why can’t sperm be produced using the cell cycle?

The cell cycle produces new body cells, not new gametes, and sperm is a gamete (also haploid).

Why is mitosis important?

Results in new cells for growth, repair or asexual reproduction.

How do body cells become cancer cells?

Mutations in the DNA cause cells to divide uncontrollably, forming a tumour.

What processes in animals result in growth and development?

Mitosis and differentiation

Chart to monitor growth in animals

Percentile chart

Percentile

Boundaries that show which percentage of a population will be within a certain growth range at different stages of their life.

Cell differentiation

Where cells that can become any cell (stem cells) become specialised and change to perform a specific function.

Neurones

Cells specialised for neurotransmission

Fat cells

Cells specialised with liposomes to store fat

Muscle cells

Specialised to have proteins that contract and shorten

Red blood cells

Specialised with haemoglobin to carry oxygen

Processes in plants that lead to growth and development

Mitosis, elongation and differentiation

Where does mitosis occur in plants?

Meristem - In the tip of the root and shoot

Cell elongation

After cells are made in the meristem, they elongate, to allow the plant to grow taller, or towards light and away from gravity.

How to measure plant growth?

Change in length of a feature or change in mass of the whole organism.

Where differentiation happen in plants?

After the zone of elongation and the meristem there is a zone of differentiation, where plant cells become specialised.

Why do meristematic cells have many ribosomes and mitochondria?

Ribosomes - to make proteins needed for new cells

Mitochondria - to release energy used in cell division

Embryonic stem cells

Found in embryos and can differentiate into any cell.

Adult stem cell

Found in adult tissues, are involved in growth and repair, but can only become a narrow range of cells (they’re part specialised).

Advantages of stem cell treatments

Stem cells can replace damaged cells not able to be repaired.

Very effective for some treatments e.g. bone marrow transplants.

Disadvantages of stem cells for growth treatments

May cause cancer so extensive testing is required before application.

May be rejected by the immune system.

How do impulses cross synapses?

The impulse reaches the axon terminus, which cause the release of a neurotransmitter, which diffuses across the gap and causes an impulse in the next neurone.

Neurotransmitter

A chemical released at a synapse to keep an impulse going.

Importance of synapses

They ensure one way neurotransmission and coordination

Synapses

A gap between neurones

Importance of reflex arcs

They allow more rapid response without the impulse having to reach the brain to make a decision, which could save your life.

Describe a reflex arc

Receptor → sensory neurone → relay neurone → motor neurone → effector

Function of motor neurones

Carry impulses to muscles for contraction

Relay neurones

Link sensory neurones and motor neurones in reflex arcs

Sensory neurones

Carry impulses to the brain and spinal cord

Myelination

The myelin sheath is a fatty layer around the axons of neurones. It insulates the axon and speeds up neurotransmissions, ensuring they reach their desired location quickly.

Where are the different neurones found?

Sensory - in the body - linking receptors to the brain

Relay - in the brain and spinal cord

Motor - in the body - linking brain to muscles

Nervous system

The system, made of cells called neurones, that coordinate fast communication throughout the body.

Central nervous system

The brain and spinal cord. The rest is the peripheral nervous system.

Consequences of reduced myelination

No insulation mean impulses travel more slowly/less frequently so muscle contraction doesn’t happen in a controlled way.

Describe the structure of a sensory neurone

Describe a relay neurone

Describe a motor neurone

What is a nerve impulse (neurotransmission)?

An electrical signal that is carried by the neurone

Stimulus

A change in the environment around you

Receptor

A cell that detects stimuli

Response

Something that an organism does once it detects the stimulus

Effector

Something that does the response - a muscle or gland.