S Flashcards
Sclerotic
The tough, white outer layer of the eye which keeps it in shape.
Secretion
The release of useful substances by cells.
Selective breeding
see artificial selection
Self-pollination
The transfer of pollen grains from the anther of a flower to the stigma of the same flower or a different flower on the same plant.
Sense organs
A receptor organ that is sensitive to a particular stimulus or stimuli, e.g. touch, light, sound, temperature and chemicals.
Sensitivity
The ability to detect changes in the environment and make responses.
Sensory neurones
A neurone that transmits impulses from receptors to the brain or spinal cord.
Sex chromosomes
The pair of chromosomes that determine a person’s sex chromosome, In humans, XX is female and XY is male.
Sex linkage
The location of a gene on a sex chromosome, usually the X chromosome.
Sexual reproduction
The process involving fusion of haploid nuclei to form a diploid zygote and the production of genetically dissimilar offspring.
Sexually transmitted infection
A disease that is transmitted through body fluids during sexual activity, e.g. HIV.
Sickle cell anaemia
An inherited disease affecting haemoglobin, which alters the shape of the red blood cells and results in severe anaemia.
Small intestine
The region of alimentary canal that completes digestion and absorbs digested food.
Solute
A substance that dissolved in a solvent.
Solvent
A liquid that dissolved substances.
Species
A group of organisms with similar characteristics which are capable of interbreeding and producing fertile offspring.
Sperm
the male sex cell or gamete.
Starch
An insoluble carbohydrate made from glucose molecules. An energy store in plant cells and an important component of the human diet.
Stem
The organ that supports the leaves, flowers and fruits of a plant. It contains xylem tissue to transport water and mineral salts and phloem tissue to transport sugars and amino acids.
Stem cells
Unspecialised cells that divide by mitosis to produce daughter calls that can become specialised for specific functions.
Stimulus
A change in the environment that is detected by a sense organs.
Stoma (Stomata)
a small hole in the epidermis of leaves that allows gases to diffuse in and out. The size of the hole is controlled by the guard cell.
Stomach
A muscular sac at the end of the oesophagus that mixes food with gastric juice. The chemical digestion of protein begins in the stomach.
Suspensory ligaments
Fibres that hold the lens in the eye in place and alter its shape when the ciliary muscles contract and relax.
