Biology GCSE Revision

Cells and Control

The Process

Interphase

• Cell replicates organelles and chromosomes
• Each chromosome is made up of 2 sister chromotids.

Early Prophase

• Chromosomes condense and become visible
• Both sister chromotids joint at the centromere.

Late Prophase

• Nuclear membrane dissipates &  spindle fibres form.
• These attach to centromere of chromosome at poles of cell.

Metaphase

• Spindle fibres pull chromosome to line up on equator of cell

Anaphase

• Spindle fibres contract.
• Chromotids pulled apart and move to poles of cell.
• CHROMOTIDS ARE NOW CHROMOSOMES

Telophase

• New nuclear membranes form around both groups of chromosomes at each pole

Cytokinesis

• Cytoplasm divides.
• 2 new cells are formed.

Mitosis: The process of cells dividing to produce two diploid daughter cells that are genetically identical to the parents.

Diploid: Have two copies of each type of chromosome. Humans have 23 pairs of chromosomes.

• Mitosis produces identical cells for:

=>growth

=>repair of damaged cells & worn out tissue

=>asexual reproduction (in strawberries and aphids).

Asexual Reproduction: Producing new organisms from one parent only. They will be genetically identical to the parent.

• The offspring are clones & no variation
• Faster than sexual reproduction

• Mitosis is the production of two daughter cells
• Each with identical sets of chromosomes in the nucleus to the parent cell
• => Formation of two genetically identical diploid body cells.

• Cancer cells are produced through uncontrollable cell division
• Produces tumours that damages the body and results in death.
• Benign: not harmful
• Malignant: dangerous (when moving through metastatis).

Growth: A permanent increase in the no. of cells or in the mass or size of an organism (normally by mitosis).

• Nerve Cell=>2m long to carry messages around body.
• Sperm Cell=> Tail to swim
• RBC=> No nucleus for more space for Oxygen.

Why is cell differentiation important for specialised cells?

Differentiation: Where an unspecialised cell turns into a very specific cell, with a specific functions and specific adaptations, it has become specialised. 

• Having specialised cells allows multicellular organisms to work more efficiently.

Percentile Charts

• Used to assess a child's growth over time to overall pattern in development can be seen
• No. of babies will have that specific mass but be below the percentile line.
• Draw lines from age and mass and see where they meet.

• Plants tend to grow at their tips of roots and shoots - meristems
• These are zones of cell division - mitosis
• Then the cell goes through elongation (cell walls loosen links between celluslose molecules) to allow water in => expansion of vacoule and cytoplasm.
• The links reform and walls become rigid again.
• Cells then differentiate into specialised cells that have different functions.

Types of Plant Cell

Meristem

• Undifferentiated cells in plants
• Can become any type of cell

Specialised Cells 2

Root Hair Cell

• Large surface area to take in more water.
• Thin cell wall to allow easy net movement of water
• No mesophyll (chloroplast tissue)

Palisade Cell

• Contain chloroplasts to help plant make food by photosynthesis.
• Found in the top of the leaf
• Large surface area to catch as much sunlight as possible

Specialised Cells 3

Xylem Cell

• Consist of dead cells
• Thick strengthened cell wall with hollow middle
• Involved in movement of water through a plant.

Guard Cells

• Found either side of stomata pores on underside of leaf
• Control opening and closing of pores during different times of day and different conditions
• Able to change shape=> opening and closing of pores

Stem Cells: An unspecialised cell that continues to divide by mitosis to produce more stem cells and other cells that differentiate into specialised cells.

• Stem cells are found in early human embryos and in adult bone marrow (or specific places).

Pluripotent: Can become any cell type

Multipotent: Can only become a limited no. of cells.

Adult Stem Cell

• Tissues created from these will not be rejected by the body.

Embryonic Stem Cell

• Found in inner cell mass in the blastocyst.

Meristems

• Can produce any type of specialised cell
• Shoot => Apical Meristem
• Root/Stem => Lateral Meristem
• Middle of the Stem => Intercalary Meristem

Medecine

• Can treat many diseases caused by damaged cells like Diabetes I, leukemia and CVD.
• If stem cells continue to divide in the body => cancer
• They can be rejected.
• They can be used to test new drugs on

Brain: The central processing centre of the body

• If there is no activity in the medula oblongata => brain-dead

CT Scans

• X-ray scan
• Beams move in a circle around the head
• Detectors measure the absoprtion of the X-ray
• 3D picture of the brain
• Diagnose conditions
• Moniter conditions after diagnosis

PET Scans

• Positron Emission Tomography
• Patient is injected with radioactive glucose
• The more active the cell, the more glucose it will absorb => respiration
• Radioactive atoms release gamma rays which can be detected by a scanner.
• Shows changes in real time
• Useful for studying disorders that change the brain's activity.

Spinal Cord Problems

• Adult Stem cells do not differentiate into neurones in the spinal cord
• Wires are used to stimulate nerves and muscles in quadriplegics.

Brain Tumours

• Brain tumours can squash parts of the brain and stop it working.
• Cells can be killed by radiotherapy (high energy X-ray beams) and chemotherapy (drugs).
• These can damage body and brain
• Chemo might not work due to blood-brain barrier (natural filter that only allows certain substances from the blood to the brain).

Limitations of CNS Surgery

• Hard to repair damage - no way to repair nervour tissue
• Not possible to surgically remove tumours growing in certain parts of the brain
• Surgery could lead to permanent damage

• The nervous system is made up of the brain, spinal cord, nerves and sense organs

Detecting Stimuli

• A stimulus stimulates a response in the body
• Detected by receptor cells in sense organs
• Receptor cells create electrical signals called impulses.
• Impulses travel from the receptor cells to the brain (voluntary response) or spinal cord (reflex action/ involuntary response) sent along
• Brain processes this and sends impulses to effectors (muscles & glands) to carry out an action. 

Adaptations

• Sensory Neurone: Long dendrites => quicker impulse than using many.
• Motor Neurone: Myelin sheath => Electrical Insulator => speeds up impulse
• Relay Neurone: Long Axon => quicker impulse.

Synapses

• An electrical impulse travels along an axon and to the ends of the neuron.
• End of first neuron releases chemicals =>neurotransmitters
• Chemicals diffuse across synapse (gap) and bind to receptors in 2nd neuron
• Receptors in 2nd neurone only bind with specific chemicals from the first.
• 2nd neurone is stimulated and transmits an electrical impulse down the axon.
• Slowed down because diffusion takes time

Reflex Arc

• If in danger: signals go from sensory to motor via relay
• Skips CNS but goes through unconscious part of brain.
• The reflex is from receptor to effector

Adaptations

Cornea

• Thick layer to protect the eye

Iris

• Its muscles contract and relax to alter the size of the pupil.

Rod and Cone Cells

• The photoreceptors are sensitive to black and white and colour. 
• Cone cells function in bright light and produce detailed vision
• Rod cells function in low light and movement

Common Defects

Cataracts

• Protein build-up inside the lens and makes it cloudy.
• Full vision can be restored by using a plastic lens.

Colour-blindness

• Cones don't work properly and cannot be corrected.
• Most common is red-green colour blindness.

Short-sightedness

• Distant objects appear blurred
• Rays focused in front of retina because the eyeball is too long or cornea is too curved.
• Can be solved using a diverging lens.

Long-sightedness

• Caused by eyeball being too short or cornea being less curved.
• Can be fixed by converging lens