https://filestore.aqa.org.uk/resources/biology/specifications/AQA-8461-SP-2016.PDF n
Cell structure & transport (B1
Microscopes and Magnification
● Magnification → how much bigger the image is than the actual specimen
● Resolution → the ability to distinguish between 2 points
● Light microscopes have: stage, light, fine focus, course focus, objective lens (x10 - x40),
eyepiece lens (x10)
● Total magnification = eyepiece lens x objective lens
● Light microscopes are: cheap, portable, and you can see in colour and look at live cells.
They have relatively low magnification, and low resolution.
● Electron microscopes are: more detailed, can magnify up to 2,000,000 and can see in
3D. but you can only look at dead cells, and in black and white. They are very expensive
and not portable.
● Calculating magnification: remember equation triangle with image size on top, and actual
size and magnification on the bottom.
Eukaryotic and prokaryotic
● Eukaryotic cells → have cytoplasm, cell membrane and have their genetic material
contained within a nucleus.
● Prokaryotic cells (bacteria) → have a cell wall as well as cytoplasm and a cell
membrane, but DO NOT have their genetic material contained within a nucleus.
●
Feature Animal Plant Bacteria
Nucleus ✅ ✅ ❌material
(loop of genetic
instead)
Cytoplasm ✅ ✅ ✅
Cell membrane ✅ ✅ ✅
Cell wall ❌ ✅ ✅
Ribosomes ✅ ✅ ✅
, Mitochondria ✅ ✅ ❌
Chloroplast ❌ ✅ ❌
Size (μm) 10 - 30μm 10 - 100μm 1μm
● Binary fission → a form of cell division where a bacterial cell will replicate by asexual
reproduction to form clones. It happens by everything inside the cell duplicating, and
increasing in size, eventually then splitting into 2.
● Some prokaryotic cells (bacteria) also have a slime capsule, plasmid (rings of DNA), and
flagellum (to help swim).
Specialised Cells
● Nerve cell: conduct electrical impulses
- Dendrites - branch-like structures to connect with other nerve cells
- Axon - long, conducts electrical impulse in one direction
- Myelin sheath - acts like a coating to insulate the impulse
- Synapses - found at the end of the cell, send neurotransmitter chemicals to
another nerve cell or effector
● Sperm cell: travel towards and fertilise an egg
- Nucleus contains half the full chromosomes number (other half is in the egg cell)
- Long tail - helps to swim towards eggs
- Lots of mitochondria - to transfer energy to the tail to swim faster
- Acrosome - contains enzymes to break through the egg’s outer layer
● Muscle cells - contract
- Special proteins - slide past each other making muscle fibres contract
- Many mitochondria - to transfer energy for these contractions
- Glycogen - to store energy in the form of glucose
● Root hair cell - absorb water and mineral ions from the soil
- Long hair-like extension to increase surface area for absorption
- Many mitochondria - to fuel the active transport of minerals into the cell
- Large permanent vacuole - for water to move into by osmosis
- No chloroplasts - no sunlight’s going to reach them
● Xylem cells - transport water and mineral ions from the roots to the leaves
- Made from dead cells and the cell walls have broken down between them
forming hollow tubes strengthened by lignin
● Phloem Cells - transport the products of photosynthesis (glucose) from the leaves to the
rest of the plants
, - Made from living cells where the cell wall has broken down between cells to form
sieve plates that allow sugars to flow freely by translocation
- Companion cells are found either side of phloem cells that have many
mitochondria to transfer energy to phloem cells
Diffusion, osmosis & active transport
● Diffusion: net passive movement of particles from an area of high concentration to an
area of low concentration.
● Examples of diffusion:
- Oxygen and carbon dioxide in gas exchange
- Waste products like urea from cells into blood plasma in kidney for excretion
● Factors which affect the rate of diffusion:
- Concentration gradient
- Surface area to volume ratio
- Temperature
● How organisms are specialised for exchanging materials:
- Large surface area
- Thin membrane/walls - less distance for diffusion
- Having efficient blood supply
- Being ventilated
● Osmosis → diffusion of water from a dilute solution to a concentrated solution, through a
partially permeable membrane
● Active transport → moves substances from an area of low → high concentration,against
the concentration gradient requires energy from respiration
● Hypertonic → higher solute concentration
● Hypotonic → lower solute concentration
● Turgid → cell is about to burst
● Flaccid/plasmolysed → shrivelling
Required Practical: use of a light microscope to observe, draw and label a selection of
plant and animal cells
plant cells:
● Use tweezers to peel off a single layer of onion skin
● Lay it flat on top of a clean microscope slide, with no air bubbles
● Dye the cells with a drop of iodine to make it clearer to see
● Use a mounted needle to lower a coverslip over it, with no air bubbles
● Clip it onto the stage and adjust the microscope accordingly, starting from the lowest
power, and then zoom in to focus in on specific parts.
Animal cells:
● Use a cotton bud, to swab the inside of your cheeks to extract cells
, ● Rub the cotton bud onto the centre of a clean microscope slide
● Add a drop of methylene blue stain, to make you see it better
● Use a mounted needle to lower a coverslip over it, with no air bubbles
● Clip it onto the stage and adjust the microscope accordingly, starting from the lowest
power, and then zoom in to focus in on specific parts.
Drawing and labelling:
● For the onion, it should look like tessellated rectangles, with a dot for the nucleus on the
left.
● You should label the cell wall, the nucleus and the cytoplasm. Also include the total
magnification.
● For the cheek cells, it should look like hexagonal kinda splodges, randomly spaced.
● You should label the cell membrane, nucleus and cytoplasm. Also include the total
magnification.
● Low plan drawing, would just be a simple overview of the tissue, labelling the parts and
different cells.
● High plan drawing, would be the cell zoomed in, with the subcellular structures labelled.
Culturing Microorganisms
Required practical - growing bacteria
● Wash your hands with antibacterial soap and clean your work surface with disinfectant
● If you work closely to a bunsen flame then there will be no bacteria in that area
● To transfer the bacteria onto your agar jelly in your petri dish, you must take your
inoculating loop and hold it in the bunsen flame, until it is red hot. Allow it to cool, and dip
it into your bacterial culture
● Transfer the bacteria to the surface of your agar, by gently scraping in a zig-zag motion
all across the agar jelly.
● Since bacteria prefer warmer conditions, we put it in an incubator. We close the petri
dish, and tape it. This is so that bacteria cannot get in or out, leaving a clean culture of
ONLY the bacteria we swabbed on. However, oxygen can still go in. We also label it with
what bacteria it is we are attempting to grow, and the day we inoculated it.
Bacterial growth
● Over the next few days, the bacteria will experience something called a “lag phase”, this
is where there is not much growth as such, but the number of bacteria does not fall.
● Then through binary fission, the bacteria multiply and grow in number.
● It will get to a peak where the number of bacteria plateaus again. This could be due to:
lack of food, competition for space, and toxins produced by the bacteria.
● Therefore the population of bacteria will start to die down again.
Cell structure & transport (B1
Microscopes and Magnification
● Magnification → how much bigger the image is than the actual specimen
● Resolution → the ability to distinguish between 2 points
● Light microscopes have: stage, light, fine focus, course focus, objective lens (x10 - x40),
eyepiece lens (x10)
● Total magnification = eyepiece lens x objective lens
● Light microscopes are: cheap, portable, and you can see in colour and look at live cells.
They have relatively low magnification, and low resolution.
● Electron microscopes are: more detailed, can magnify up to 2,000,000 and can see in
3D. but you can only look at dead cells, and in black and white. They are very expensive
and not portable.
● Calculating magnification: remember equation triangle with image size on top, and actual
size and magnification on the bottom.
Eukaryotic and prokaryotic
● Eukaryotic cells → have cytoplasm, cell membrane and have their genetic material
contained within a nucleus.
● Prokaryotic cells (bacteria) → have a cell wall as well as cytoplasm and a cell
membrane, but DO NOT have their genetic material contained within a nucleus.
●
Feature Animal Plant Bacteria
Nucleus ✅ ✅ ❌material
(loop of genetic
instead)
Cytoplasm ✅ ✅ ✅
Cell membrane ✅ ✅ ✅
Cell wall ❌ ✅ ✅
Ribosomes ✅ ✅ ✅
, Mitochondria ✅ ✅ ❌
Chloroplast ❌ ✅ ❌
Size (μm) 10 - 30μm 10 - 100μm 1μm
● Binary fission → a form of cell division where a bacterial cell will replicate by asexual
reproduction to form clones. It happens by everything inside the cell duplicating, and
increasing in size, eventually then splitting into 2.
● Some prokaryotic cells (bacteria) also have a slime capsule, plasmid (rings of DNA), and
flagellum (to help swim).
Specialised Cells
● Nerve cell: conduct electrical impulses
- Dendrites - branch-like structures to connect with other nerve cells
- Axon - long, conducts electrical impulse in one direction
- Myelin sheath - acts like a coating to insulate the impulse
- Synapses - found at the end of the cell, send neurotransmitter chemicals to
another nerve cell or effector
● Sperm cell: travel towards and fertilise an egg
- Nucleus contains half the full chromosomes number (other half is in the egg cell)
- Long tail - helps to swim towards eggs
- Lots of mitochondria - to transfer energy to the tail to swim faster
- Acrosome - contains enzymes to break through the egg’s outer layer
● Muscle cells - contract
- Special proteins - slide past each other making muscle fibres contract
- Many mitochondria - to transfer energy for these contractions
- Glycogen - to store energy in the form of glucose
● Root hair cell - absorb water and mineral ions from the soil
- Long hair-like extension to increase surface area for absorption
- Many mitochondria - to fuel the active transport of minerals into the cell
- Large permanent vacuole - for water to move into by osmosis
- No chloroplasts - no sunlight’s going to reach them
● Xylem cells - transport water and mineral ions from the roots to the leaves
- Made from dead cells and the cell walls have broken down between them
forming hollow tubes strengthened by lignin
● Phloem Cells - transport the products of photosynthesis (glucose) from the leaves to the
rest of the plants
, - Made from living cells where the cell wall has broken down between cells to form
sieve plates that allow sugars to flow freely by translocation
- Companion cells are found either side of phloem cells that have many
mitochondria to transfer energy to phloem cells
Diffusion, osmosis & active transport
● Diffusion: net passive movement of particles from an area of high concentration to an
area of low concentration.
● Examples of diffusion:
- Oxygen and carbon dioxide in gas exchange
- Waste products like urea from cells into blood plasma in kidney for excretion
● Factors which affect the rate of diffusion:
- Concentration gradient
- Surface area to volume ratio
- Temperature
● How organisms are specialised for exchanging materials:
- Large surface area
- Thin membrane/walls - less distance for diffusion
- Having efficient blood supply
- Being ventilated
● Osmosis → diffusion of water from a dilute solution to a concentrated solution, through a
partially permeable membrane
● Active transport → moves substances from an area of low → high concentration,against
the concentration gradient requires energy from respiration
● Hypertonic → higher solute concentration
● Hypotonic → lower solute concentration
● Turgid → cell is about to burst
● Flaccid/plasmolysed → shrivelling
Required Practical: use of a light microscope to observe, draw and label a selection of
plant and animal cells
plant cells:
● Use tweezers to peel off a single layer of onion skin
● Lay it flat on top of a clean microscope slide, with no air bubbles
● Dye the cells with a drop of iodine to make it clearer to see
● Use a mounted needle to lower a coverslip over it, with no air bubbles
● Clip it onto the stage and adjust the microscope accordingly, starting from the lowest
power, and then zoom in to focus in on specific parts.
Animal cells:
● Use a cotton bud, to swab the inside of your cheeks to extract cells
, ● Rub the cotton bud onto the centre of a clean microscope slide
● Add a drop of methylene blue stain, to make you see it better
● Use a mounted needle to lower a coverslip over it, with no air bubbles
● Clip it onto the stage and adjust the microscope accordingly, starting from the lowest
power, and then zoom in to focus in on specific parts.
Drawing and labelling:
● For the onion, it should look like tessellated rectangles, with a dot for the nucleus on the
left.
● You should label the cell wall, the nucleus and the cytoplasm. Also include the total
magnification.
● For the cheek cells, it should look like hexagonal kinda splodges, randomly spaced.
● You should label the cell membrane, nucleus and cytoplasm. Also include the total
magnification.
● Low plan drawing, would just be a simple overview of the tissue, labelling the parts and
different cells.
● High plan drawing, would be the cell zoomed in, with the subcellular structures labelled.
Culturing Microorganisms
Required practical - growing bacteria
● Wash your hands with antibacterial soap and clean your work surface with disinfectant
● If you work closely to a bunsen flame then there will be no bacteria in that area
● To transfer the bacteria onto your agar jelly in your petri dish, you must take your
inoculating loop and hold it in the bunsen flame, until it is red hot. Allow it to cool, and dip
it into your bacterial culture
● Transfer the bacteria to the surface of your agar, by gently scraping in a zig-zag motion
all across the agar jelly.
● Since bacteria prefer warmer conditions, we put it in an incubator. We close the petri
dish, and tape it. This is so that bacteria cannot get in or out, leaving a clean culture of
ONLY the bacteria we swabbed on. However, oxygen can still go in. We also label it with
what bacteria it is we are attempting to grow, and the day we inoculated it.
Bacterial growth
● Over the next few days, the bacteria will experience something called a “lag phase”, this
is where there is not much growth as such, but the number of bacteria does not fall.
● Then through binary fission, the bacteria multiply and grow in number.
● It will get to a peak where the number of bacteria plateaus again. This could be due to:
lack of food, competition for space, and toxins produced by the bacteria.
● Therefore the population of bacteria will start to die down again.
