Cell Structure notes

Unit 1.1.1 in F111 for OCR Biology AS-Level

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Cell Structure
Prokaryotes and Eukaryotes
There are two main types of organism ­ eukaryotes and prokaryotes. Prokaryotic organisms
are prokaryotic cells (i.e. singlecelled). Eukaryotic organisms are made up of eukaryotic
cells.
Organelles
Organelles are parts of cells. Each one has a specific function. If you examine a cell through
an electron microscope you can see its organelles and internal structure ­ this is known as
the cell ultrastructure.
Plant Cell:
Animal Cell:

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Organelle Diagram Description Size/distr
Thin boundary
Around all
Cell membrane between cell and
most org
environment
A large organelle
surrounded by a
nuclear envelope
(double membrane), About 1
Nucleus which contains many diameter, u
pores. The nucleus per c
contains chromatin
and often a structure
called the nucleolus
Dark staining region in Usually one
Nucleolus (see above)
the nucleus but occasion
It is usually oval
shaped.…read more

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A group of fluidfilled
flattened sacs. Found in the
Golgi Apparatus Vesicles are often close to th
seen at the edges of endoplasmic
the sacs
Either floats
cytoplas
attached to
A very small dense endoplasmic
Ribosomes
organelle
Size = 2
diame
(80
A rigid structure that
surrounds plant cells.
Cell wall Surrounds al
It's made mainly of the
carbohydrate cellulose
A small, flattened
structure found in plant
cells. It's surrounded
by a double
membrane, and also
has membranes inside
called thylakoid
membranes.…read more

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A round organelle
surrounded by a
Lysosome Float in the
membrane with no
clear internal structure
A small fluidfilled sac
surrounded by a
membrane. Some are
formed by the Golgi
Found in the
Vesicle apparatus or the
or near the
endoplasmic reticulum
while others are
formed at the cell
surface
Small, hollow
cylinders, containing a Usually foun
Centriole
ring of microtubules nucle
(tiny protein cylinders)
Small, hairlike
structures.…read more

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Eukaryotes and Prokaryotes
Eukaryotes = `true nucleus' (Greek)
Examples include:
Animal cells
Plant cells
Fungal cells
Their main features are:
Large (80s) ribosomes
Nucleus
Membrane bound organelles
Prokaryotes ­ `no nucleus' (Greek)
Examples include:
Bacterial cells
Their main features are:
`naked' DNA (not contained in the nucleus)
Very few organelles (these are not membrane bound)
Small (70s) ribosomes
Comparing Eukaryotes and Prokaryotes
Eukaryotic Animal Eukaryotic Plant
Prokaryote Cells
Cells Cells
Extremely small
Larger cells (2 ­
Size (less than 2µm
200µm diameter)
diameter)
Largest organelle…read more

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Small (70s)
Large (80s)
Ribosomes ribosomes always
ribosomes
free in the cytoplasm
Made of
Cell wall peptidoglycan (or Absent Made of cellulose
murein)
Not 9+2 microfibril
arrangement 9+2 microfibril
Flagella Absent
(different internal arrangement
structure)
Gametes (egg and Egg and pollen divide
sperm) divide by by meiosis. Growing
Cell division Binary fission
meiosis.…read more

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The Cytoskeleton
The organelles in cells are surrounded by the cytoplasm. The cytoplasm is more than just a
solution of chemicals ­ it's got a network of protein threads running through it. These protein
threads are called the cytoskeleton. In eukaryotic cells the protein threads are arranged as
microfilaments (small solid strands) and microtubules (tiny protein cylinders).
The cytoskeleton has four main functions:
1. The microtubules and microfilaments support the cell's organelles, keeping them in
position
2.…read more

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Protein production
Cells within some organisms produce hormones (chemical messenger molecules that help
coordinate the activities of the whole organism. E.g. auxins in plants and insulin in animals).
1. The instructions to make the hormone are in the DNA in the nucleus
2. The specific instruction to make the hormone is known as the gene for that hormone.
A gene is on a chromosome
3. The nucleus copies the instructions in the DNA onto a molecule called mRNA
4.…read more

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Micrometre (µm) 0.001 mm
Nanometre (nm) 0.000001 mm
To convert a smaller unit to a bigger unit you divide by 1000.
Resolution
Resolution is how detailed the image is. More specifically, it's how well a microscope
distinguishes between two points that are close together.
Types of microscope
Light microscopes ­ they use light. They have a lower resolution than electron
microscopes. They have a maximum resolution of about 0.2µm. The maximum magnification
of a light microscope is about x1500.…read more

Comments

Kelsey

Great notes just what i needed! Thankyou :-D

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