MAKING SENSE OF
CELLS
IGCSE Biology
1.1 Life Processes – Cells
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• Can you remember the processes in MRSGREN that
are common to most living things?
• Can you recognise cell structures such as the
nucleus, cytoplasm, cell membrane, cell wall,
chloroplast and vacuole, and describe their
functions?
• What are the major differences between plant and
animal cells?
• MRS GREN stands for the 7 characteristics of living
things.
• All living organisms from a simple bacteria to plants
and animals, can do all of these processes.
MOVEMENT
• Animals move by the action of muscles
• Plants: Slow growth movement called a
tropism
RESPIRATION
• Releasing energy from food consumed
SENSITIVITY
• To respond to stimuli: which means they are
sensitive to changes in their surrounding.
GROWTH
• Increasing the size of cells and the number of
cells
REPRODUCTION
• Reproduce: to produce offspring and increase
the number of own species
EXCRETION
• Excrete: removal of waste products from
cellular metabolism
HOMEOSTASIS
• Control their internal environment
NUTRITION
• Plants: they make their own food by
Photosynthesis.
• Animals: Eat other organisms
MAKING SENSE OF
CLASSIFICATION
IGCSE Biology
1.2 The Variety of Living Organisms
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• Can you describe the common features shared
by organisms within the following main
groups: plants, animals, fungi, bacteria,
protoctists and viruses?
• What does the term ‘pathogen’ mean?
• Understand that pathogens may be fungi,
bacteria, protoctists or viruses.
• All living organisms can be classified into
groups based on certain criteria.
• One of the simplest forms of classification is to
split all living things into 5 Kingdoms.
• Animals, plants, fungi, protoctists and
bacteria.
• We will also look at viruses which are nonliving and therefore classified separately.
• They are multicellular.
• Cells contain chloroplasts.
• Carry out photosynthesis and therefore make
their own food (autotrophic).
• Have cellulose cell walls.
• Store sugar as starch.
• They are multicellular.
• Get their nutrition from feeding on other
organisms (heterotrophic).
• They are capable of movement.
• Store sugar as glycogen.
• Can be multicellular or unicellular.
• Cell wall made of
.
• Made of a network of fibres called a
of
.
• Feed by
nutrition using
enzymes.
• A strange collection of simple organisms that
do not fit into the other groups therefore
often known as the ‘dustbin’ kingdom.
• Mostly single celled.
• E.g. protozoa like amoeba or Algae.
• Small single celled organisms.
• Three basic shapes: spheres, rods and spirals.
• Cell wall made of polysaccharides and
proteins (peptidoglycan).
• Some have a capsule or slime layer.
• Has no nucleus.
• Some species have flagella.
• Some contain plasmids (loops of DNA) which
we can use in genetic engineering.
• All are parasites.
• Much smaller than bacteria cells.
• Not made of cells, and do not carry out any of
the normal ‘characteristics’ of living
organisms.
• Made of genetic material surrounded by a
protein coat.
• All natural viruses cause disease.
• It could be a virus e.g. influenza.
• It could be a fungus e.g. athlete’s foot
• It could be a bacteria e.g. cholera
• It could be a protoctists e.g. malaria
• These pathogens can often be passed from person to
person.
PLANT CELLS V/S ANIMAL CELLS
Plant Cells
Animal Cells
1. Plant cells have a cell wall made
up of cellulose
1.
Animal cells do not have a cell
wall.
2.
2.
Animal cells do not have
chloroplasts.
Plant cells have chloroplasts
containing chlorophyll.
3. Plant cells have large permanent 3.
vacuoles containing cell sap.
4.
Plant cells store carbohydrates
in the form of starch.
4.
Animal cells have small temporary
vacuoles.
Animal cells store carbohydrates
in the form of glycogen.
Functions of the parts of cells
Part of cell
Function
Cell wall
Protects, supports and gives a fixed shape to plant cells.
Totally permeable.
Cell membrane
Controls the substances that enter and exit the cell.
Selectively permeable.
Cytoplasm
Jelly like fluid – living material in which many chemical reactions
take place. Surrounds all organelles.
Nucleus
Controls all activities of the cell. Contains genetic information
(DNA)
Chloroplast
Contains the pigment chlorophyll which absorbs light for
photosynthesis.
Vacuole
Stores sell sap – solution of water with dissolved sugars, mineral
ions and other solutes.
LEVELS OF ORGANISATION
 Organelles are found in cells.
Cells form tissues.
 Tissues form organs.
 Organs form organ systems.
 Organ systems form organisms.
Levels of Organisation
• In your copy book organize the following
terms in order from:
• smallest (bottom)  largest (top).
• Organs
• Organ systems
organism
Tissues
• Cells
organelles