Edexcel GCSE Biology Topic 2

Gene

short section of DNA codes for a protein and controls characteristic

Gametes

sex cells with half the number (23) of chromosomes

Cell Cycle

series of steps cell must undergo to divide

Interphase

1^st stage in cell cycle. cell grows, organelles like ribosome and mitochondria increase in size and number, protein synthesis occurs, DNA replicates, forming X shape, energy stores increased

Mitosis

2^nd stage of cell cycle. chromosomes line up at cell equator. cell fibres pull each chromosome to either side of the cell.

Cell Equator

where chromosomes line up during mitosis

Cytokinesis

3^rd stage of cell cycle. cytoplasm, cell membranes divide. 2 identical daughter cells

Daughter Cells

2 identical cells produced by mitosis, with identical sets of chromosomes to parent cell

Genetically Identical Cells

cells produced by mitosis with same sets of chromosomes as parent cell

Cell Differentiation

cells develop into specialised forms adapted to their function

Specialised Cells

cells with structure adapted for specific function e.g. muscle, blood

Cell Division in Mature Animals

mostly to repair or replace damaged cells, little growth

Elongation

plant cells grow longer in specific direction, absorb water into vacuoles, controlled by auxins

Asexual Reproduction

type of reproduction where 1 organism replicates own cells to produce offspring

Stem Cells

cells retain the ability to differentiate, replace specialised cells which can’t divide

Red Blood Cells

specialised cells, lose nucleus, cannot divide, replaced by adult stem cells

Differentiation in Plants

many types of cells retain the ability to differentiate throughout life, differentiating only when reaching final position in plant

Cancer

result of small changes in cells leading to uncontrolled cell division

Tumour

group of cells results from uncontrolled cell division

Percentiles charts

used to measure rate of organism growth

Growth Measurement: Babies

mass, length, head circumference.

50th Percentile: Mass

heavier than 50% of babies

25th Percentile: Mass

heavier than 75% of babies

75th Percentile: Mass

heavier than 25% of babies

High Percentile

90th percentile or higher can indicate health problem

Stem Cell

undifferentiated cell can divide to produce many more similar cells, some of which will differentiate

Embryonic Stem Cells

egg and sperm cell fuse, forming zygote, differentiate into any type of cell in the body

Adult Stem Cells

in bone marrow, can form many types incl. blood cells

(Plant) Meristems

in root and shoot tips, can differentiate into any type of plant and retain this ability across plant lifespan

Cloning (Plants)

meristems used to make clones of the plant, necessary for desirable features, save from extinction

Therapeutic Cloning

produce an embryo with the same genes as patient, harvest embryonic stem cells

Advantages of Therapeutic Cloning

not rejected, exact same genetic make-up as the patient

Benefits of Stem Cell Research

replace damaged or diseased body parts

Problems of Stem Cell Research

don’t completely understand differentiation process, hard to control stem cells to form desired cells

Ethical Objections to Stem Cell Research

religious or ethical objections, interference with the natural process of reproduction

Contamination Risk in Stem Cell Research

if growing stem cells are contaminated with a virus, infection can be transferred to the individual

Central Nervous System (CNS)

brain and spinal cord, control consciousness, movements, thoughts, emotions

Cerebral Hemispheres

takes up most of skull, sitting on the left and right sides

Cerebrum

These two parts are known as the cerebrum and perform a huge variety of functions, including consciousness, memory, intelligence as well as visual and sensory processing.

Cerebellum

large 'lump-like' structure found at bottom of the brain, on rear side. controls fine muscle movements, can move in complex ways

Medulla Oblongata

small 'elongated' structure, in brainstem, at base of brain. maintains basic autonomic ('automatic) bodily functions: breathing, digestion, swallowing, sneezing.

CT Scan

fire X-Ray radiation at brain from several angles, generate 3D image. examine bleeding within skull, damage to brain structures

PET Scan

radioactive 'tracer' is injected into blood pre-scan. scan is sensitive to tracer. areas of tracer build-up i.e. clotting, inflammation, highlighted more brightly

Reflexes

automatic responses occurring before you time to think, prevent individual from getting hurt

Reflex Arc

pathway allows vital responses to occur quickly. different from typical response to stimuli, impulse doesn’t pass through conscious areas of brain

Sensory Neurons

cells carry electrical impulses from receptor cells to the central nervous system (CNS)

Motor Neurons

cells carrying electrical impulses from the CNS to effectors

Effectors

muscles or glands that enact response to stimulus

Synapses

gaps between two neurons

Cancerous Tumours

can form in the brain as in any other part of the body, resulting from changes in cells leading to uncontrolled cell division.

Brain Function Investigation Challenges

complex + delicate, easily damaged, drugs cannot always reach brain

Electrical Impulse

signal travels along neurons allowing communication within nervous system.

Receptor Cells

convert stimulus into electrical impulse

Relay Neuron

in CNS, impulse passes to relay neuron, helps transmit signal.

Stimulus

change in environment, can provoke a response

Glands

effectors which secrete hormones in response to stimuli

Pupils Reflex

pupils getting smaller, avoid damage from bright lights

Hand Withdrawal Reflex

moving hand from hot surface to prevent damage

Brain Injury Examination

examine brain tissue for injury and disease, non-invasive methods, CT and PET scans

CT Scan: Risks + Contraindications

CT usually not recommended for pregnant women and children, higher doses of radiation than normal X-ray

Use Case: PET Scan

PET useful for identifying cancerous tumours, which use more blood than normal tissue

Neurotransmitter

chemical released into synapse when impulse reaches end of first neuron

Synapse

neurotransmitters diffuse across this gap to trigger impulses in next neuron

Myelinated Nerves

nerves surrounded by myelin sheath, faster nerve transmission

Myelin

produced by Schwann cells, surrounds nerves, speeds up action potential

Action Potential

nerve transmission, travels faster in myelinated nerves

Accommodation

process, eye changes shape to focus on near or distant objects

Retina

layer light sensitive cells at back of eye, sends impulses to brain, creating image

Rod Cells

cells in retina, more sensitive to light, better for seeing in low light

Cone Cells

cells in retina, colour vision

Cornea

see-through layer at front of the eye, bends, focuses light onto retina

Iris

ring of muscles surrounding pupil which control its size by contracting or relaxing

Ciliary Muscles

muscles holding lens in place, control shape for focusing

Suspensory Ligaments

structures holding lens in place, help control shape

Lens

transparent, curved surface reflects light onto the retina

Cataracts

clouding of the eye’s lens, restricts vision, treated by lens replacement surgery

Colour Blindness

inability to see certain colours, lack of cone cells in retina

Spectacle Lenses

lenses correct vision, concave lenses for myopia, convex lenses for hyperopia

Contact Lenses

lenses work like glasses but allow for activities like sport, available in hard or soft types

Laser Eye Surgery

procedure treats myopia or hyperopia with lasers to alter corneal thickness or curvature

Replacement Lens

artificial clear plastic lens, replaces natural lens, treat hyperopia

Anaphase

3^rd stage of mitosis. chromatids pulled to opposite cell poles by spindle fibres

Axon

long fibre conducts nerve impulses away from cell body

Cataract

cloudy patch forms on eye’s lens of the eye.
prevents light from entering normally
blurred vision, difficulty seeing intensity of colours, problems with glare.
surgery swaps clouded lens for a synthetic plastic one

Cerebral hemisphere

One half of the cerebrum. The left hemisphere controls muscles on the right side of the body and vice versa.

Chromatid

'arm' of replicated chromosome.

Chromosome

long, coiled DNA molecule carrying genetic information, genes

Dendrites

short, branched extensions of dendrons. large surface area receives nerve impulses from other neurones

Dendron

branched extensions of nerve cell body. connect to other neurones, carry impulses towards body

Diploid cell

cell with 2 copies of each, full set, 46 chromosome(s)

Effector

organ, tissue, or cell producing response to a stimulus

Eye

sense organ. receptors sensitive to light intensity and colour

Growth

increase in mass or size

Haploid cell

cell with single copy of each / half the number of / 23 chromosome(s)

Hyperopia / Long-Sightedness

eye defect, nearby objects appear out of focus, convergence of light rays behind retina. too-short eyeball or less elastic lens. corrected with convex lens

Meristem tissue

plant tissues containing undifferentiated stem cells

Metaphase

2^nd stage of mitosis: chromosomes align at the cell equator

Motor neurone

neurone carries nerve impulses from CNS to effectors

Myelin Sheath

electrically insulating layer surrounding axon, increases speed of nerve impulses

Neurones

nerve cells adapted to quickly transmit nerve impulses. functional units of nervous system