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Class notes edexcel IGCSE (9-1) biology unit 1 life processes
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BiologyLife Processes
, Ñ All living organisms are made of cells
Ñ Cell = basic functional unit of an organism
Ñ Unicellular = a microscopic organism made from a single cell
(the simplest organism)
Ñ Multicellular = an organism composed of millions of cells (more
complex)
Ñ In multicellular organisms, there may be hundreds of different
types of cells, different structures, specialized to carry out
different functions
Ñ E.g.: humans are made up of kidney cells, liver cells, muscle
cells, brain cells etc., carrying out different functions
Characteristics of living things:
Ñ Despite all the differences, there are basic features that are the
same in all organisms:
Ñ M = movement
Ñ R = respiration
Ñ S = sensitivity (sense)
Ñ G = growth
Ñ R = reproduction MRS GRENC
Ñ E = excretion
Ñ N = nutrition
Ñ C = control of internal environment
Ñ Movement:
An action by which an organism changes position/place
Action of muscles in animals contraction
Slow growth movements in plants – e.g.: leaves, shoot and
growing upwards to gain more sunlight
To obtain food
To avoid predators
Ñ Respiration:
Happens in cells
The chemical reaction that releases energy from the
breakdown of nutrients/food e.g.: glucose
Glucose + oxygen carbon dioxide + water + energy
But respiration is not breathing
, Breathing = taking air in the lungs
Ñ Sensitivity:
The ability to sense and detect changes/stimuli in their
surroundings (external and internal) and respond to them
Example: response to stimulus: light (when entering a dark
room, the pupil dilates), sound, touching something very
hot, smell and taste
Sensitivity in plants: e.g.: gravity pulling the roots down and
sunlight pulling the shoot up
Sense organs detect these stimuli: nose, tongue, ears, eyes
Ñ Growth:
Increase in size, mass, and complexity, using materials from
their food
Increasing number (by cell division) and size of cells
When respiration takes place, it provides excess energy for
cells to divide and grow
Ñ Excretion:
Removal of toxic waste products from the body e.g. carbon
dioxide (by respiration), urea, sweat: waste products of
metabolism
Metabolism = all chemical reactions taking place in the body
How? (excretory organs)
Lungs: carbon dioxide
Kidneys: urea
Skin: sweat
Ñ Nutrition:
Taking in nutrients which are organic substances (hydrogen
& carbon, e.g.: carbohydrate protein) or mineral irons (e.g.:
calcium, sodium, iron) for growth, repair, and energy
Ñ How?
Animals by ingestion (taking in nutrients), eat other
organisms heterotrophs
Plants make their own food by photosynthesis
autotrophic organisms
Ñ Control of internal conditions:
, Maintenance of a steady state within a narrow range inside
the body = homeostasis
Examples:
Body temperature
Fluid balance
pH (=7)
Concentrations of ions e.g.: calcium for bones and sodium
for neurons
Blood sugar levels e.g.: if homeostasis doesn’t happen and
sugar levels increase, it can result to diabetes
Cell structure – animal cell:
Ñ Animal cells are eucaryotic since they have a nucleus
surrounded by a cell membrane
Ñ Cell structure of higher/complex organisms:
Nucleus
Cytoplasm
Cell membrane
Ñ Red blood cells
have no nucleus or
chromosomes but
they’re still
eucaryotic cells
Ñ They don’t have a
nucleus because
they require an
increased capacity to transfer more oxygen (function of a red
blood cell)
Ñ Cytoplasm:
Function of the cytoplasm = where all chemical reactions are
happening
Living material that makes up a cell that is enclosed by the
cell membrane
Sloppy jelly-like texture (something between a solid and a
liquid)
, Complex material made of many different structures,
organelles e.g.: nucleus, ribosomes, and mitochondria
Organelles = specialized subunits within the cytoplasm that
have specific functions
But organelles are so small; you can only see them with an
electron microscope that has a higher magnification
Ñ Nucleus:
Largest organelle in a cell
Function of the nucleus = center of chemical activity, plays a
major role in determining the size, shape, and function of
the cell: controls the activities of the cell
Almost all cells have a nucleus
Some exceptions - e.g.: cells that are dead: xylem vessels in a
stem or cells that don’t live very long: red blood cells (120
days)
Xylem vessels = transfer water/ they need increased capacity
to transfer more water
Contains chromosomes (46 in human cells) which carry the
genetic material or genes
Each chromosome is made up of 1 DNA molecule and 1
protein. The DNA’s divided into smaller parts known as
genes
Genes = control the activities and functions of the cells by
determining which proteins the cell can make and therefore
the characteristics of each individual by instructing the
production of a specific protein
DNA is found and remains in the nucleus, but the
instructions for making proteins are carried out of the
nucleus to the cytoplasm, where proteins assemble on tiny
structures = ribosomes
Ribosomes are the sites of protein synthesis, e.g.: enzymes =
a group of proteins that speed up chemical reactions that
take place in the cytoplasm
Thousands of ribosomes in cells
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