Edexcel GCSE 9-1 Biology - SB2: Cells and Control

Paper 1 Specification: https://qualifications.pearson.com/content/dam/pdf/GCSE/Science/2016/Specification/GCSE_Biology_Spec.pdf

What is mitosis?

• part of the cell cycle (process of growth and repair produced in cell cycle)

• the process of cells dividing to produce two diploid daughter cells that are genetically identical to the parent

What are the stages of mitosis?

PROPHASE: nucleus begins to break down and spindle fibres appear

METAPHASE: by the end of metaphase, chromosomes are lined up on the spindle fibres across the middle of the cell

ANAPHASE: the chromosome copies are separated and moved to either end of the poles on the spindle fibres

TELOPHASE: membrane forms around each set of chromosomes to form nuclei

CYTOKINESIS: cell surface membrane forms to separate the two cells

the copies of the chromosomes separate and each daughter cell ends up with the same number of chromosomes as the parent cell

Describe the importance of mitosis in growth, repair and asexual reproduction

growth: no. of cells within an organism increase by mitosis, basic of growth in multicellular organisms

repair: regeneration, some animals are able to regenerate whole parts of their body => production includes mitosis, healing process of a wound includes mitosis

asexual reproduction: mitosis allows many species to undergo asexual reproduction => production of new individuals of a species by the parent organism

What does cancer result in?

cancer is a result of changes in cells, leading to uncontrolled cell division (excess amount of cells)

Describe growth in organisms

growth happens by mitosis, v often when young till full growth

younger animals: cell division at a faster rate => more growth

mature animals: mostly used for repair

PLANTS: 1st in meristem (end of shoots/roots due to rapid cell division) occurs due to cell elongation zone due to osmosis in vacuoles

Explain the importance of cell differentiation in the development of specialised cells

• differentiation produces specialised cells, adapted/specialised to carrying out specific functions

• make up a whole multi-cellular organism + specialised cells make them work more efficiently

What are percentile charts used for?

• divided into 100 groups

• finds % of readings below a percentile

• curved lines show rate of growth at the same percentile

  • remains near the same percentile curve

  • % increase = (final*initial)/initial * 100

What are the functions of embryonic stem cells and stem cells in animals?

ESC:

• taken from embryo at early stages of division

• produce any type of specialised animal cell

• repair/replace brain cells (Parkinson’s) retina cells (blindness) grow transplants/drug testing tissue

adult SC:

• differentiated tissue in an animal (bone marrow)

• stem cells lose ability to produce other specialised cells (fully developed)

• only produce surrounding tissue stem cells

• treat leukaemia (bone marrow cancer) + potentially new tissues genetically matched to patients

What are the functions of meristems in plants?

PLANT MERISTEM CELLS:

• taken from rapidly growing parts (roots/shoots)

• divide + differentiate to produce any type of specialised plant cells (only if plant lives)

• can be used to clone rare plants facing extinction

• clone crop plants for farmers with desirable traits (selective breeding)

What are the benefits and risks of the use of stem cells in medicine?

positive: replace faulty diseased cells with healthy specialised cells + stimulate growth

negatives: rejection of cells from another person, cancer

What are the functions of the cerebellum, cerebral hemispheres and the medulla oblongata?

CEREBELLUM: balance, posture, muscle coordination, fine motor skills

CEREBRAL HEMISPHERES: voluntary movement, senses, consciousness, languages, memory, behaviour

MEDULLA OBLONGATA: automatic activities => breathing, heart rate, reflex control

What are CT and PET scans?

CT:

• detectors measure x-ray absorption

• shape differences can be linked to behaviour so functions can be worked out if the area has lost function

PET:

• patients are given radioactive glucose

• more active cell take in more glucose, detected as radioactivity causes gamma rays

• activities cause specific areas of the brain to become more active

Which limitations are present when treating damage + disease in the brain and other parts of the nervous system?

SPINAL CORD: reduces flow of neurons between brain + body parts

can lead to loss of use of legs and/or arms

no adult stem cells can differentiate into neurones => specialised so can’t divide to replace damaged cells

BRAIN TUMOURS: cancer cells divide rapidly to form tumours

radiotherapy + chemo can kill cancer but damage healthy cells

chemo may not work due to blood-brain barrier only allowing certain substances to pass (hard to access)

Explain the structure and functions of:

• sensory neurones

• motor neurones

• relay neurones

sensory neurones: carry impulses from receptor cells to CNS

motor neurones: carry impulses from CNS to effectors

relay neurones: carry impulses between neurones and makes up as tissue

Explain the structure and function of fatty myelin sheaths

fatty myelin sheaths:

• surround long dendrons ± axons

• insulate neurones from neighbouring n’s so doesn’t lose energy

• makes an impulse jump along the cell between the gaps in the myelin => speeds up neurotransmission

Explain the structure and function of synapses

synapses:

• gaps between 2 neurones

• when nerve impulse reaches axon terminals at the end of a neuron/axon, impulse causes another chemical to be released into gap and diffuse across it

• fits into receptors and generates new impulse in next neuron

Explain the structure and function of neurotransmitters

• slow down neurotransmission

• only released from one axon terminal to ensure direction of flow

• lets fresh impulses to be generated in neurones connected to one neurone so the original impulse doesn’t split and lose strength

  • without it, electrical impulses can’t cross synaptic gaps

Explain the structure and function of a reflex arc

• neurone pathway

• from receptor to effector bypassing parts of the brain used to process info

• when a stimulus is detected by receptor cells, an impulse is created

• that impulse travels along a sensory neurone

• released neurotransmitters diffuse across the gap and generate an impulse in the relay neurone and is transmitted along it

• impulses transmitted across the motor neurones axon to the effector

• brings out a rapid response (muscle communication)

Explain the structure and functions of the eye as a sensory receptor

cornea: refracts light rays entering onto a point in the retina

lens: refracts and focuses to form a sharp image on retina

iris: controls amount of light entering the pupil, constricts to protect cones + rods at day (circular muscles contract) and dilate to let more light in at night

rod cells: sensitive in low light intensity- differences in light intensity

cone cells: sensitive in bright light- responds to RGB colour changes

Describe defects of the eye

cataracts: cloudy, protein build up in lens, light cannot pass through properly =>blurs image on retina

long-sightedness: focus on distant, blur close objects, eye too short, light focuses behind retina

short-sightedness: focus on close, blur distant objects, eye too long, light focuses in front of retina

colour-blindness: cone cells don’t work properly, difficulty seeing colour

Explain how defect of the eye can be corrected

cataracts: replace cloudy lens with artificial (plastic) lens

long-sightedness: converging lens (bending light ray before reaching the eye)

short-sightedness: diverging lens (spreading out light rays before reaching the eye)