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.
Appreciate that it is important that dissolved substances
must be able to
get in and out of a cell through the cell membranes, otherwise the cell could
not live or reproduce!
Cells can be either eukaryotic or
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.
Prokaryotes, are smaller and
simpler prokaryotic cells and single celled organisms (unicellular) eg
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.
ANIMAL CELLS including humans! (eukaryotes)
Most animal cells
have the following five parts - subcellular structures, and, remember,
plants cells usually have the same five components too.
1. Cell membrane
The cell contents i.e.
the 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. The cell membrane allows the free passage of water and gases but may
act as a barrier to other chemicals.
The energy releasing
chemistry of 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.
Mitochondria are power house of the cells
and provides 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 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
contains the instructions for making proteins eg that make up tissue or
The ribosomes are where protein synthesis
from amino acids occurs in the cell. They are too small to be seen by a
Stored food for
Some animal cells may have several small vacuoles
Some differences between animal and plant cells
Animal cells are much larger than bacterial
cells, with important differences from plant cells.
Animal cells do not have (i) a rigid cell wall, (ii) a
permanent vacuole and (iii) chloroplasts.
PLANT 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.
The three principal differences between them is that most
plant cells have (i) a rigid cell wall, (ii) chloroplasts and (iii) a permanent
vacuole, which animal cells do NOT have.
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.
chloroplasts, which absorb light energy to
make food via chlorophyll in photosynthesis
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.
(ii) Chloroplasts the sites of
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.
Stored food for
respiration from the glucose made by photosynthesis.
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 - the cell contents i.e. the
cytoplasm, DNA etc. are all held together within the cell wall surface
membrane which controls
the passage of substances in and out of the cell.
Cytoplasm - 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.
Bacterial cells, single-celled microorganisms, are much smaller than plant
or animal cells with some quite distinct and different features.
Chromosomal DNA - the genetic material
genes are not in a distinct true nucleus, the genetic material is a sort of jumbled cluster
comprising of one long strand of
DNA, sometimes in the form of connected loops floating in the cytoplasm.
The single chromosome that 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
Plasmids are small hoops
of extra DNA that are separate from the chromosomal DNA.
Plasmids contain genes that help tolerance
against drugs and can be passed from one bacteria to another.
This is how the dangerous bacteria MSRA have
Bacteria come in all sorts of shapes eg rods, spirals
etc. and some have a tail!
The flagellum is a long
thin tail 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!
It is quite a remarkable piece of
biochemical engineering - bioengineering!
(d) 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.
(e) CELL SPECIALISM - a few examples
Know and understand that cells may be specialised to carry out a
particular function e.g.
Red blood cells to carry oxygen
via their haemoglobin molecules.
White blood cells of the immune
Gamete cells ie egg cells and
sperm cells are the sexual reproduction cells.
Palisade leaf cell structure is
adapted to support the sites of photosynthesis.
Guard cells can open and close
the pores (stomata) in leaves - they must allow oxygen and carbon dioxide to
pass in and out.
- use and development
Plant and animal cells can be studied in greater detail
with a light microscope.
Microscopes enable you to objects (like
microorganisms) which you cannot see with the naked eye.
Microscopes using the visible part of the
electromagnetic spectrum (visible light) were invented in the late 16th
century and the optical lens systems have been improved through the
following centuries even until today.
With these light microscopes you can see
individual cells and smaller details such as nuclei and mitochondria in all
cells, and chloroplasts in plant cells.
Changes in microscope technology have enabled us to see
cells with more clarity and detail than in the past, including simple
In the 20th century, with advances in atomic
physics, the electron microscope was invented which works off beams of
electrons instead of visible light.
This has enabled the magnification produced
by a microscope to be considerably increased to the point where you can see
even smaller structures such as the internal details of mitochondria,
chloroplasts and plasmids (hoops of DNA).
magnification = length of image / length of
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