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GCSE Biology RevisionCells
Cells
Prokaryotes and Eukaryotes
Prokaryotes - simple, single celled organisms
Eukaryotes - complex, multi-celled organisms
Animal cells
Contain:
- Nucleus, controls all activities of the cell and contains genetic information needed to
create new cells
- Mitochondria, where aerobic respiration takes place
- Cytoplasm, liquid gel in which the organelles are suspended in, where the majority of
reactions needed for life take place
- Cell membrane, controls the transfer of substances in and out of the cell
- Ribosomes, where protein synthesis takes place
Plant Cells
Contain:
- All the bits that animal cells have
- Rigid cellulose cell wall, strengthens and supports the cell
- Permanent vacuole,space in the cytoplasm to filled with cell sap to maintain the cell's
structure for the plant
- Chloroplasts, contains chlorophyll so that photosynthesis can occur
Bacterial Cells
They are prokaryotes, they only have 1 cell and have only a single strand of dna in the
cytoplasm
Cell Differentiation to Become Specialised
Differentiation is the process by which a cell changes to become specialised
Specialised cells are cells which have developed subcellular structures allowing them to
carry out specific functions e.g root hair cells and sperm cells
Stem Cells
Stem cells are undifferentiated cells which have the potential to specialise into anything
Some people are against the use as it's using a potential human life (embryo) in each
experiment
However many people are for using them as it has potential to cure many diseases as faulty
faulty cells can be replaced via specialization of other stem cells
Chromosomes and Meiosis
The nucleus is made up of chromosomes, which are made up of genes which control
characteristics
Body cells have two pairs of chromosomes, one from the mother and one from the father,
that's how variation occurs
,Each cell contains 46 chromosomes, however in meiosis the chromosomes duplicate (like
mitosis) then crossing occurs where genetic information is exchanged (thus variation occurs)
and it divides twice to 4 diploid cells (23 chromosomes)
Mitosis and the Cell Cycle
Mitosis produces an identical cell and is used in Asexual reproduction
Firstly in the cell the chromosomes double and move to opposite ends of the cell, the cell
splits and forms two new cells with 46 chromosomes each
The cell cycle is what a cell goes through in its existence, it grows and replicates DNA and
then duplicates through mitosis
Evolution
Any evolution question:
Mutation
Advantage
Competition
Reproduction
Variation
Every species had variation
Different genes cause variation through alleles from the two gametes are fused and
determine characteristics depending on the combination
The environment also causes variation such as living conditions affecting its growth
Mutations occur randomly and may change certain characteristics, some of which may have
a competitive advantage
Evolution
Theory of Evolution - all of today's species have evolved from simple life forms that first
started to develop over 3 billion years ago
Charles Darwin discovered this from his travels around the Galapagos islands and the
similar species which were varied due to the different conditions on the different islands
Fossils and genetics help support this and now we know how mutation occurs
Development of a new species is called speciation, occurs when population change so much
that they become reproductively isolated where they can’t interbreed
Extinction is when no individuals of a species remain
Based on natural selection, fittest pass on jeans
Selective Breeding
Where humans artificially select the plants or animals that are going to breed so that genes
for particular characteristics remain in the population
Over several generations all animals will have this characteristic, it's used in agriculture and
and other businesses
This results in a reduction of the gene pool which results in them being closely related, this
means that harmful genetic defects can occur from interbreeding
Genetic engineering
,To transfer a gene responsible for desirable characteristics from one organism's genome to
another's
Process includes isolating a gene from a genome using enzymes and put in a vector, vector
is introduced to target organism and the useful gene is transferred
Cloning
We can clone plants via Tissue culture and from Cuttings
Tissue culture is where few plant cells are put in a growth medium with hormones, they grow
into new plants (clones of parent plant), can be made quickly with minimal space year long
Cuttings include taking cuttings from a parent plant and then plan them to produce
genetically identical copies, these can be produced quickly and cheaply
Animal clones can be cloned using Embryo Transport and Adult cell cloning
Sperm cells are taking from one organism and egg cells from another and splitting the
embryo many times before any spells specialise, these embryos are then placed in the
mother organisms to grow genetically identical offspring, normally used to produce offspring
from the best of each species
Adult cloning involves taking the nucleus from an unfertilised egg cell, then a nucleus is
taken from an adult body cell and placed in the egg cell, egg cell is then stimulated by an
electric shock so it divides, then the embryo is implanted into an adult female to grow
Theory of Evolution
Theory of Evolution - all of today's species have evolved from simple life forms that first
started to develop over 3 billion years ago
Charles Darwin discovered this from his travels around the Galapagos islands and the
similar species which were varied due to the different conditions on the different islands
Fossils and genetics help support this and now we know how mutation occurs
Development of a new species is called speciation, occurs when population change so much
that they become reproductively isolated where they can’t interbreed
Extinction is when no individuals of a species remain
Evidence for Evolution
Fossils
A fossil is the preserved remains or trace of a dead organism.
Fossils can be formed in several ways:
- Dead animals and plants can be preserved in amber - hardened tree resin - peat
bogs, tar pits, or in ice.
- Casts or impressions, such as footprints, can be covered by layers of sediments.
These eventually become rock, so preserving the casts.
- Hard body parts, such as bones, shells and leaves, can be covered by layers of
sediments. Over time the parts are gradually replaced by minerals.
1`1
Fossils provide a record of organisms that lived a long time ago. They also provide evidence
that animals and plants can change over long periods of time however fossil records are
often incomplete.
Extinction
Extinction is when no individuals of a species remain, this can be due to a loss of habitats,
food source or being hunted
, Resistant Bacteria
Bacteria sometimes develop random mutations in their DNA these can lead to changes in
the bacteria characteristics e.g being less affected by particular antibiotic this can lead to
antibiotic resistant strains forming
As bacteria reproduces so quickly it means that they evolve quickly as well so if the
antibiotics kill all bacteria apart from the ones which are resistant theythen reproduce and
multiply
It's not that antibiotics actually cause resistant they created situation when natural resistant
bacteria having advantage and so increase in numbers
Classification
Classification is organising living organisms into groups
Traditionally organisms have been classified according to a system first proposed in the
1700s by Carl Linnaeus
Kingdom, phylum, class, order, family, genus, species
Organisms are named according to the binomial system in this system every organism is
given its own two part Latin name the first part refers to the genus the second part refers to
the species e.g Homo sapiens
Evolutionary trees show evolutionary relationships and common ancestors between living
and extinct animals
Cell Transport
Diffusion
Diffusion is the net movement of particles along a concentration gradient from an area of
high concentration to an area of low concentration
Diffusion happens in both Solutions and gases this is because particles in the substances
are free to move about randomly
The bigger the concentration gradient the faster the diffusion rate
A higher temperature will also give a faster diffusion rate as the particles have more energy
The larger the surface area of the membrane the faster the diffusion rate as more particles
can pass through at once
Osmosis
Osmosis is the net movement of water molecules across a partially permeable membrane
from a region of higher water concentration to a region of lower water concentration
Just like diffusion water molecules move randomly and pass through both ways of
membrane
The greater the concentration gradient the faster the rate of osmosis
A higher temperature results in a faster rate of osmosis
A larger the surface area of a membrane also results in a faster rate of Osmosis
Active transport
When substances need to be absorbed against a concentration gradient in 230 was active
transport e.g root hairs for taking minerals and water
Active transport needs energy from respiration to make it work unlike diffusion
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