Download Revision summary 1. Cells, life processes, variety of living

Revision notes on cells, life processes and living organisms
CHARACTERISTICS OF LIVING ORGANISMS
1.1
recall that living organisms share the following basic characteristics
Movement
Muscles in animals, directional growth in plants, flagella in
bacteria
Respiration
Release energy from food
Sensitivity
Responding to changes in the environment
Growth
Increase in size and mass
Reproduction
Producing offspring (more of the same kind of organism)
Excretion
Getting rid of toxic waste
Nutrition
Taking in or producing their own food
Control of internal conditions
Keeping internal conditions constant, e.g body
temperature
VARIETY OF LIVING ORGANISMS
1.2
Describe common features shared by organisms within the groups: plants, animals,
fungi, bacteria, protoctists and viruses, and describe examples and their features in
each group
Plants
Plants are multicellular organisms
Examples include flowering plants, such as a cereal (for example maize) and a herbaceous legume (for
example peas or beans).
Plants contain chloroplasts and are able to carry out photosynthesis
Plants have cellulose cell walls. The cell wall and the vacuole together give the cell its shape and
maintain turgor (stiffness) to support the plant (see point 2.14)
Plants store carbohydrates as starch or sucrose. Starch is stored in the leaf and the root; sucrose is
transported in the phloem (see point 2.51)
Animals
Animals are multicellular organisms
Examples include mammals (e.g. humans) and insects (e.g. housefly and mosquito).
Mammals keep a constant body temperature and are vertebrates (have a backbone)
Insects are invertebrates
Animals do not contain chloroplasts and are not able to carry out photosynthesis: animals
are heterotrophic – they consume other organisms for their nutrition
Animals usually have nervous coordination and are able to move from one place to another
Animals have no cell walls and they often store carbohydrate as glycogen
Revision notes on cells, life processes and living organisms
Fungi
Fungi are not able to carry out photosynthesis; many are multicellular; some, like yeast, are single-celled.
Their body is usually organised into a mycelium of
thread-like structures called hyphae, which contain
many nuclei; the hyphae feed by excreting digestive
enzymes onto food material and absorbing the organic
products; this is known as saprotrophic nutrition
Fungi have cell walls made of chitin; they may store
carbohydrate as glycogen.
Examples include mucor (green-blue mould) which
reproduces using spores, and yeast, used to make bread or
beer.
Bacteria
Bacteria are microscopic single-celled organisms with no
nucleus (are prokaryotes).
Examples: Lactobacillus bulgaricus, a rod-shaped
bacterium used to make yoghurt from milk, and
Pneumococcus, a spherical bacterium that causes
pneumonia.
Bacteria have a cell wall, cell membrane, cytoplasm and
plasmids (rings of extra DNA: see points 5.12, 5.13).
Bacteria DNA is in a large loop called the chromosome.
Most bacteria feed off other living or dead organisms
(saprotrophic nutrition). A few bacteria can carry out photosynthesis.
Protoctists
Protoctists are microscopic single-celled organisms. They are
complex cells with a nucleus and other organelles. They are not animals
or plants because each cell is an individual organism, not part of a
multicellular organism.
Some protoctists, like Amoeba, have features like an animal
cell. Others, like Chlorella, have chloroplasts and are more like
plants.
A pathogenic protoctist, Plasmodium, is responsible for
causing malaria (see point 1.30)
Viruses
Viruses are small particles, smaller than bacteria; they are parasites and can reproduce only inside
living cells; they infect every type of living organism.

Examples include the tobacco mosaic virus that causes discolouring of the leaves of
tobacco plants by preventing the formation of chloroplasts, the influenza virus that causes
Revision notes on cells, life processes and living organisms
‘flu’ and the HIV virus that causes AIDS (see point 1.30).
1.3

Viruses have a variety of shapes and sizes; they have no cellular structure but have a protein coat
and contain genetic material - either DNA or RNA.

Apart from reproduction, viruses do not perform any of the life processes (MRSGRENC)
Recall the term ‘pathogen’ and know that pathogens may be fungi, bacteria,
protoctists or viruses.
Pathogen: an organism that causes disese like a virus, fungus or bacterium.
Viruses are responsible for AIDS and 'flu; bacteria can cause pneumonia; malaria is caused by a
protoctist; Athlete's foot (Fusspilz) is a fungal infection (see point 1.2)
NB white blood cells provide defence against pathogens: phagocytes are non-specific,
lymphocytes are specific (see point 2.61)
SECTION 2: STRUCTURES AND FUNCTIONS IN LIVING ORGANISMS
A) LEVELS OF ORGANISATION
2.1
Describe the levels of organisation within organisms: organelles, cells, tissues,
organs and systems.
ORGANISM < ORGAN SYSTEM < ORGAN < TISSUE < CELL < ORGANELLE < BIOLOGICAL MOLECULE
Biological molecule – molecule made
by organisms and used in life processes,
e.g. respiration
Examples: DNA, proteins, lipids, starch, glucose,
amino acids, haemoglobin, enzymes
Organelles - structures within a cell that
carry out specific functions
Examples: nucleus, chloroplast, mitochondria
(see point 2.20, 2.30)
Cells - the basic structural and
functional unit from which all biological
organisms are made
Examples of specialized cells include nerve cells,
sperm cells, root hair cells and palisade
mesophyll cells
Tissues - a group of specialized cells,
which are adapted to carry out a
specific function
Examples include muscle tissue, nerve tissue,
palisade mesophyll tissue (in leaves)
Organs - a collection of two or more
tissues, which carries out a specific
function or functions
Examples include the heart, brain, spinal cord,
liver, kidneys, lungs, bladder, small intestine,
pancreas and stomach; in a plant the leaf is an
example of an organ.
Organ Systems - a group of two or more Examples include the circulatory system,
nervous system, endocrine system and digestive
organs
system.
Revision notes on cells, life processes and living organisms
B) CELL STRUCTURE
2.2
Recognise cell structures, including the nucleus, cytoplasm, cell membrane, cell wall,
chloroplast and vacuole
2.3
Describe the functions of the nucleus, cytoplasm, cell membrane, cell wall,
chloroplast and vacuole
2.4
Nucleus structure: at the centre of the animal cell
and between the vacuole and cell membrane in a
plant cell. Contains DNA
Nucleus function: Controls cell
activities
Cell membrane structure: selectively permeable
boundary of the cell
Cell membrane function: Controls
what substances go in and out of cell
Cytoplasm structure: a jelly-like substance that fills
the cell and contains enzymes
Cytoplasm function: site of most of
the chemical reactions in the cell.
Chloroplast structure: contain a green pigment
called chlorophyll. (Only plant cells)
Chloroplast function: Absorb light
energy to make (food)glucose by
photosynthesis
Cell wall structure: made of cellulose or chitin
which surrounds the cell membrane (Only plant
cells)
Cell wall function: rigid structure that
gives the cell support and strengthens
it.
Vacuole structure: largest part of plant cell, in the
centre; contains cell sap, a store of dissolved
sugars and minerals. (Only in plants)
Vacuole function: fills with water and
maintains turgor to support the plant
Describe the differences between plant and animal cells.
Both contain a nucleus, cytoplasm and a cell membrane
Animal cells do not have a cell wall, central vacuole or chloroplasts (see point 2.30)