Introduction to plant & animal CELL STRUCTURE
Doc Brown's Biology Revision Notes
Suitable for GCSE/IGCSE/O level Biology/Science courses or equivalent
All living things are made up of cells,
the building blocks of life.
A cell is the smallest unit of life able
to control its own activities, BUT, it relies on the rest of the
organism (if multicellular) or the surroundings (if unicellular) to
provide it with raw materials i.e. nutrients and removal of waste
You should know and understand that the structures of different types of
cells are related to their functions.
You should know and understand the similarities and
differences between animal cells, bacteria and plant cells.
Cells can be either
prokaryotic in character.
Eukaryotes are organisms made of
eukaryotic cells, which are complex cells, and all plants and animals are
made up of such cells. They are usually multi-cellular organisms, but can
consist of one cell e.g. yeast.
Plant and animal cells (eukaryotic cells) have a
cell membrane, cytoplasm and genetic material
enclosed in a nucleus.
Prokaryotes, are smaller,
simpler and single celled organisms (unicellular) eg
bacteria are prokaryotic cells.
The different parts of a cell are referred to
as subcellular structures.
A diagrammatic comparison of animal
cells, plant cells and bacteria cells
- their similarities and differences in
ANIMAL CELLS including humans! (eukaryotes)
Most animal cells
have the following five parts in these eukaryotic cells - the so called subcellular structures, and, remember,
plants cells usually have the same five components too.
1. Cell membrane
The cell contents i.e.
the sub-cellular structures like cytoplasm, nucleus, (small vacuoles), mitochondria etc. are all held together by
the soft cell membrane which controls the passage of substances in and out of the
cell. Because not everything can pass through the membrane, it is described
as a semi-permeable or a partially permeable membrane.
The cell membrane allows the free passage of water and gases but may
act as a selective barrier to other chemicals. The cell membrane also
contains receptor molecules that are used in cell communication e.g. by
The energy releasing
respiration occurs in the mitochondria, which is where
most energy is released in respiration - eg the aerobic 'burning' of glucose to release
e.g. glucose + oxygen ==> carbon dioxide +
water + energy
The equation of aerobic respiration, an exothermic
chemical reaction and catalysed by the appropriate enzymes.
glucose + oxygen ===>
carbon dioxide + water
+ 6O2(g) ===> 6CO2(g) + 6H2O(l)
RESPIRATION - aerobic and anaerobic in plants, fungi and animals,
conditions, substrates etc. gcse
biology revision notes
Mitochondria are the power house of the cells
and contain all the enzymes needed for the chemical reactions that provide the chemical energy for any of the cells functions.
Liver cells carry out lots of metabolic reactions
so lots of energy needed, so they contain a lot more mitochondria.
Similarly, muscle cells need lots of energy eg to
contract, so again, they have a lot more mitochondria than other cells
to supply the energy for the physical work animals perform.
Cytoplasm is a jelly like
fluid (gel-like) in which most of the cells chemical reactions take place
and most of these reactions are catalysed by enzymes (biological catalysts)
which control the rate of these reactions. Anaerobic respiration take place
in the cytoplasm, but aerobic respiration takes place in the mitochondria.
The cell nucleus contains
all the genetic material, the DNA codes of the genes in the chromosomes which control the cells
functions and the cell division in replication. The nucleus controls the
activities of the cell by sending instructions to the cytoplasm. The genetic
material is organised into chromosomes.
contains the instructions for making proteins eg that make up tissue or
Ribosomes are involved in the translation
of the genetic material from the chromosomes, they can decode the DNA to
carry out various chemical synthesis e.g. ribosomes are where protein synthesis
from amino acids occurs in the cell - the protein 'factory'! They are too small to be seen by a
Stored food for
Some animal cells may have several small vacuoles
Some differences between animal, plant and
Animal cells are much larger than bacterial
cells, with important differences from plant cells.
Animal cells, unlike plant cells, do not have (i) a rigid cell wall, (ii) a
permanent vacuole and (iii) chloroplasts.
Note: What is an
organelle? An organelle is a specialized part of a cell having some
specific function, a sort of cell organ. Organelles are only found in eukaryotes
(plant and animal cells). The nucleus, mitochondria, ribosomes and chloroplasts
are examples of organelles.
PLANT and algal CELLS (eukaryotes)
Plant cells are much larger than bacterial
cells, with important differences from animal cells.
Like animal cells, plants cells have (1) a
cell membrane, (2) mitochondria, (3) cytoplasm, (4) nucleus and (5) ribosomes,
all of which perform the same functions as described above in the animal cell
section (b) above.
The three extra principal different
sub-cellular structures that plant cells have plant
and animal cells do not are: (i) a rigid cell wall, (ii) chloroplasts and (iii) a
vacuole - animal cells do NOT have these three features.
You need to be able to describe the function
of the components of a plant cell including chloroplast, large vacuole, cell
wall, cell membrane, mitochondria, cytoplasm and nucleus (see diagram and notes
below) and know the differences between plant and animal cells.
Plant and algal cells have a
rigid cell wall made of
cellulose, which strengthens the cell, supports it and therefore the plant's structure
as a whole.
(ii) Chloroplasts the sites of
Chloroplasts can absorb light energy to
make food via chlorophyll in photosynthesis
The chloroplasts contain
the green chlorophyll molecules which are involved in the energy absorbing
photosynthesis. The chlorophyll molecules absorb the light energy
from the sun to promote the endothermic reaction below. The chloroplasts
must also contain all the enzymes to catalyse the whole series of complex
reactions to make sugars - the equation below is a greatly simplified
sunlight energy + carbon dioxide + water ==>
sugars (e.g. glucose) + oxygen
+ 6CO2(g) ====> C6H12O6(aq) + 6O2(g)
Therefore chloroplasts are the site of food
production for the plant. The sugars may be used directly as a source of
energy or converted to starch grains - the plant's food store (and part of
our food store as well!).
Chlorophyll absorbs mainly in the violet-blue and
orange-red regions of the visible spectrum, hence it appears green, the
light NOT absorbed.
(iii) Large permanent vacuole
Most plant cells have a single large permanent vacuole containing cell sap, a dilute solution of
mineral salts and sugars. It maintains the internal pressure to support the
cell. The central vacuole is a cellular organelle
found in plant cells. It is often the largest organelle in the cell. The
central vacuole is
surrounded by a membrane and functions to hold useful materials and wastes. It also
functions to maintain the proper pressure within the plant cells to provide
structure and support for the growing plant.
Stored food for
respiration from the glucose made by photosynthesis.
BACTERIA (are prokaryotes)
Bacterial cells, single-celled microorganisms, are
much smaller than plant
or animal cells with some quite distinct and different sub-cellular features.
bacterial cell consists of cytoplasm within a
membrane surrounded by a cell wall.
Bacteria do not have a real nucleus,
chloroplasts or mitochondria.
Cell wall and inner membrane
The cell contents i.e. the
cytoplasm, DNA etc. are all held together within the cell wall by the surface
membrane which controls
the passage of substances in and out of the cell. The surrounding cell wall gives
bacteria extra structural support.
The jelly like
fluid in which most of the cells chemical reactions take place with the aid
of enzyme catalysts. Although they do not have mitochondria, bacterial cells
can still respire aerobically in the cytoplasm.
Chromosomal DNA - the genetic material
is not confined in a nucleus which doesn't exist in bacteria
The genes are not in a distinct true
nucleus, the genetic material is a sort of jumbled cluster comprising of one
long circular strand of DNA floating free in the cytoplasm sometimes accompanied
one or more small rings of DNA called plasmids. As with any other cells the
string of DNA controls the cell's activities and cell division for
This single chromosome controls the
cells functions and the cell division in replication.
The chromosomal DNA moves freely around in the
cytoplasm and is not confined in a distinct nucleus as in plant and animal
Plasmid DNA, not part of the
Plasmids are small hoops
of extra DNA that are separate from the chromosomal DNA.
Plasmids contain genes that help tolerance
against drugs and this drug resistance can be passed from one bacteria to another
- a problem in dealing with bacterial infectious diseases.
This is how the bacteria MSRA have
evolved and become so dangerous.
Not all prokaryote cells contain
and Flagella (flagella plural, flagellum singular)
Bacteria come in all sorts of shapes e.g. rods, spirals
etc. and some have a tail!
The flagellum is a long
thin tail, hair-like structure that projects out of the body of the cell, and can
rotate to move the bacteria along.
Some bacterial cells have more than one
Each flagellum is effectively driven by a
tiny biochemical electric motor with moving parts, mostly made of proteins!
The flagellum enables a bacterium away
from harmful substances (e.g. toxins) and move towards beneficial materials
like nutrients or oxygen.
It is quite a remarkable piece of
biochemical engineering - bioengineering!
As with other cells, the place of protein
synthesis from decoding genetic material from chromosome material.
Other comments on prokaryotes like
Unlike eukaryotic cells, prokaryotic
cells do not contain a defined nucleus nor do they contain mitochondria or
(e) YEAST CELLS (eukaryotes)
Yeast is used in the production of
alcoholic beverages eg beer, wine etc. and in bread making.
A yeast cell, a single-cell microorganism, has a nucleus, cytoplasm,
mitochondria enclosed in a
which is surrounded by a cell wall.
CELL SPECIALISM - an introduction is on another
aqa gcse 9-1
biology: Eukaryotes and
prokaryotes : Know that plant and animal cells (eukaryotic cells) have a
cell membrane, cytoplasm and genetic material
enclosed in a nucleus. Know that bacterial cells (prokaryotic cells) are much
smaller and simpler in comparison. They have cytoplasm
and a cell membrane surrounded by a cell wall.
The genetic material is not enclosed in a
nucleus. It is a single DNA loop and there may
be one or more small rings of DNA called
plasmids. Similarities and differences between Animal and plant cells You should be able to explain how the
main sub-cellular structures, including the
nucleus, cell membranes, mitochondria,
chloroplasts in plant cells and plasmids in
bacterial cells are related to their functions.
Most animal cells have the following parts: a nucleus, which controls the activities of the
cell, cytoplasm, in which most of the
chemical reactions take place, a cell membrane, which controls the passage
of substances into and out of the cell, mitochondria, which is where aerobic
respiration takes place, ribosomes, which are where protein
synthesis occurs. Be able to recognise,
draw and interpret images of cells. In addition to the parts found in animal cells
plant cells often have: chloroplasts, which absorb light to make food
by photosynthesis a permanent vacuole filled with cell sap. Plant cells have a more rigid
cell wall. You must know the
similarities and differences between plant, animal and bacterial
cells. Plant and algal cells also have a cell wall made
of cellulose, which strengthens the cell.
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