I have compiled all of the notes that I have written up over the course of Year 12. This revision guide is catered to the AQA AS Level exam, learning and memorising the content from this booklet as well as doing past paper questions will give you a very high chance of getting an A at the end of yea...
Cell recognition and the immune system………………………….. 39
Species and taxonomy……………………………………..………. 54
Mass transport in plants…………………………………………….. 62
2
, Cells Revision:
Eukaryotes - A cell that has a membrane bound nucleus and chromosomes. It also has other
membrane bound organelles.
Prokaryotes - A cell of an organism belonging to the kingdom Prokaryotae, that is characterised by
lacking a nucleus and membrane-bound organelles.
Organelle: Description: Function: Diagram:
Nucleus: - Largest organelle, surrounded Controls cells activity –
by a nuclear envelope that through transcription
contains pores of DNA (to make proteins)
- Pores allow substances (e.g.
RNA) to move between the
nucleus and the cytoplasm
- Contains chromosomes made
from protein-bound linear DNA
- Contains structures known as
nucleolus (makes ribosomes)
Rough RER – system of membranes RER – folds and
Endoplasmic that enclose a fluid-filled space processes proteins from
Reticulum: the ribosomes
RER – surface is covered in
ribosomes
Smooth SER – similar to RER SER – synthesises and
Endoplasmic processes lipids &
Reticulum: SER – no ribosomes on surface carbohydrates
Mitochondrion: - double membrane Site of aerobic respiration
(production of ATP)
- Inner membrane is folded to
form cristae
- Inside the membranes is the
matrix (contains enzymes
involved in respiration)
- Also contains its own DNA,
proteins and lipids
3
,Golgi - Fluid filled, flattened Makes lysosomes
Apparatus: membrane sacs
Processes and packages
- Processes and packages new new lipids and
lipids and proteins proteins
- Vesicles often found at the end
of the sacs (store the lipids and
proteins & transports them out of
the cell surface membrane)
Lysosomes: - Small, round organelles These enzymes need to
surrounded by a be kept away from the
membrane cytoplasm, as they are
used to digest invading
- No clear internal structure cells/break down worn out
components
- A type of golgi vesicle
- Contain lysozymes (digestive
enzymes)
Ribosomes: - Smallest & most numerous of Site of protein synthesis
all organelles
70s (prokaryotes) or 80s
- Either float free or are attached (eukaryotes)
to the rough endoplasmic
reticulum
- Made up of proteins & RNA
- Has no clear membrane
4
,Cell - Consists of a double layer of Regulates the movement
Membrane: phospholipids (bilayer) of substances within the
cell
- Contains protein within it and
on its surface (within = channel
and carrier proteins) & (surface
= antigens & receptors)
Chloroplast: - Small, flattened structure found Site of photosynthesis
within plant and algal cells (grana and stroma)
- Contains a double membrane
- Contains circular DNA &
Ribosomes. Why?
- Stroma is an aqueous liquid
found within these membranes
(contains enzymes)
- Contains structures within
called thylakoids
- These stack up to form grana
- Grana are linked to each other
by a thin flat piece of membrane
called a lamellae
Cell Wall: - Rigid structure Provides mechanical
strength and prevent them
- Surrounds cells in plants, from changing shape due
algae and fungi to osmotic pressure
- Made mainly of cellulose (plant
and algae)
- Made of chitin in fungi
Vacuole: - Membrane bound organelles Help to maintain pressure
found within the cytoplasm of inside the cell and keep it
plant cells rigid
- The membrane is called the Involved in isolating
tonoplast unwanted chemicals in
the cell
- Contains a weak solution of
sugars and salts (cell sap)
5
, Prokaryotic Cells:
- Smaller than eukaryotic cells
- Cytoplasm lacks membrane bound organelles
- Smaller ribosomes (70S compared to 80S in
eukaryotes)
- No nucleus
- Examples include bacterial cells and
cyanobacteria
- Contain a cell wall made from peptidoglycan, a form of glycoprotein (and not cellulose)
Structure: Function:
Plasmid: ● Small circular DNA
● Contain genes (for things like antibiotic resistance)
● Not always present but some can have more of them than other
cells
Plasma membrane: ● Made mostly from lipids & proteins
● Controls movement of substances into and out of a cell
DNA (Nucleoid): ● Free floating as a long coiled strand
● Has no proteins attached to it
Cell wall: ● Formed from a polymer called peptidoglycan (murein)
● Protect against mechanical damage + osmotic lysis
● Two kinds of cell wall that can be identified using what we call a
Gram stain
6
,Ribosomes: ● Site of protein synthesis, But these are not attached to any
membranes
● They are also smaller (70S) than those in eukaryotic cells
Mesomes: ● Folded region of the membrane
● Provides a large surface area
● Contains bound enzymes required for respiration
Slime capsule: ● Thick polysaccharide layer
● sticking cells together
● As a food reserve
● Protection against outside chemicals
● Protection against phagocytosis
Flagellum: ● Helical shaped tail, for cell movement
● Embedded into the membrane & is driven by a proton (H+)
gradient
Bacterial reproduction:
- Bacteria reproduce by binary fission.
- This is an asexual process (like mitosis) which does not involve the exchange of genes.
- Can divide every 20 minutes!
Binary Fission:
The process by which prokaryotic cells divide is known as binary fission and occurs are follows:
1) The circular DNA in the cells replicates and both copies attach to the cell membrane.
Plasmids also replicate.
2) The cell membrane then begins to grow between the two DNA molecules and begins to pinch
inwards, dividing the cytoplasm in two.
3) A new cell wall forms between the two DNA molecules dividing the original cell. The identical
daughter cells each have a single copy of the circular DNA and a variable number of copies
of the plasmids.
As viruses are non-living, they do not undergo cell division – following the injection of their nucleic
acids into another cell, the infected host cell replicates the virus particles.
7
,Process:
● Replication of circular DNA. Cell contents doubles.
● Cell elongates
● Division of cytoplasm to produce 2 daughter cells each with a single copy of circular DNA
At each division, number of cells are DOUBLING, This works out as: 2n
(n = the number of divisions)
Viruses:
- Are acellular (do not have a cellular structure -
eg: no organelles)
- Viruses are not cells, they are a nucleic acid
surrounded by a protein
- They are not living (debatable)
- Viruses are neither prokaryotic or eukaryotic,
[obligate intracellular parasites]
- Viruses are even smaller than bacteria (0.1µm or
less in diameter)
- All viruses will invade and reproduce within a
host cell
Viruses are much smaller than bacteria and are acellular. They are neither prokaryotic or
eukaryotic, and are not alive. They are known as obligate intracellular parasites because they
cannot survive independently - they must infect prokaryotic or eukaryotic host cells to do so. A
virus that contains DNA is known as a virus and one that contains RNA is known as a retrovirus.
Attachment Proteins: Glycoproteins - They attach to the host cell’s surface proteins
Lipid Envelope: Outermost layer of viruses, protects the genetic material
Capsid: They protect viral nucleic acids from being destroyed by host enzymes
Matrix Structural protein linking viral envelope to virus core
Genetic Material: DNA - Virus
RNA - Retrovirus
Released in the host cell in order to multiply in quantity
8
,Viruses first attach to the cell using it’s attachment proteins, it then enters the cell and releases its
own genetic material, so when this cell reproduces, it will produce more viruses and release it into
the bloodstream (exocytosis) to further invade more cells.
Phospholipid and Cell Membranes:
The cell membrane is composed of phospholipids in which the hydrophilic heads point outwards
and the hydrophobic tails point inwards. This structure allows lipid soluble molecules to pass
through the membrane, but not water soluble molecules. It also means that the membrane is
flexible and self-sealing.
Functions:
- Controls movement of substances in/out of cells and organelles
- Internal Transport System (ER)
- Allows a cell to change shape
- Isolate damaging enzymes (such as lysozyme in the lysosome)
- Isolates organelles with specific metabolic functions
- Maintains conditions/concentrations on either side
- Provides surfaces for biochemical reactions to take place
- Forms a bilayer boundary between cytoplasm and their environment
Phospholipid Bilayer:
- Plasma membranes are mainly formed of phospholipids
- Phospholipids have a hydrophilic head and a hydrophobic tail
Hydrophilic fatty acid tails point into the middle of the bilayer to ‘protect’
them from the liquid on either side. These repel water and are NON polar
Hydrophilic polar heads point outwards. They are in contact with the
aqueous intracellular and extracellular environments. These have a strong
affinity for water and are POLAR.
9
, Phospholipid Bilayer Function:
- Allow lipid soluble substances to enter and leave the cell
- Prevent water soluble substances from entering and leaving the cell
- Make the membrane flexible (phospholipids can move laterally and change places).
Can pass through a lipid bilayer: Cannot pass through a lipid bilayer:
Fluid - Phospholipids and proteins can move around each other (laterally). This gives the
membrane flexibility.
Mosaic - Proteins and other molecules
embedded throughout the phospholipids.
Looks like a mosaic.
10
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