Studied by 45 people
What does a nucleus do?
It contains genetic material and controls the activities of the cell
What does cytoplasm do?
It's a gel-like substance where most of the chemical reactions happen. It contains enzymes that control these chemical reactions
What does a cell membrane do?
It holds the cell together and controls what goes in and out
What do mitochondria do?
These are where most of the reactions for aerobic respiration occur. Respiration transfers energy that the cell needs to work
What do ribosomes do?
This is where protein synthesis takes place - where proteins are made in the cell
What do cell walls do?
They are made of cellulose and they support and strengthen the cell
What does a vacuole do?
It contains cell sap and helps maintain the shape of the cell
What do chloroplasts do?
This is where photosynthesis occurs, which makes food for the plant. They contain chlorophyll - a green pigment - which absorbs light needed for photosynthesis
What do bacterial cells contain?
Cytoplasm, cell membrane, cell wall, flagella, ribosomes, mitochondria, slime capsule, plasmids (small rings of DNA) and a single circular strand of DNA that floats freely in the cytoplasm
What do bacterial cells NOT contain?
A nucleus
What is the equation for magnification?
Image size divided by actual size
What is differentiation?
The process by which a cell changes to become specialised for its job
What are undifferentiated cells called?
Stem cells
What are sperm cells specialised for and how are they specialised?
Reproduction - they transport the male DNA to the female DNA
-It has a flagella and a streamlined head to help it swim towards the egg
-There are lots of mitochondria in the cell to provide the energy needed
-It carries enzymes in its head to help digest through the egg cell membranes
What are nerve cells specialised for and how are they specialised?
Rapid signalling - they carry electrical signals from one part of the body to another
-They are long to cover more distance
-They have branched connections at their ends to connect to other nerve cells and form a network throughout the body
What are muscle cells specialised for and how are they specialised?
Contraction - they need to contract quickly
-They are long so they have space to contract
-They contain lots of mitochondria to generate the energy needed for contraction
What are root hair cells specialised for and how are they specialised?
Absorbing water and minerals
-They are cells on the surface of plant roots which grow into long hairs that stick out into the soil
-They have a large surface area for absorbing water and mineral ions from the soil
What are chromosomes?
Coiled up lengths of DNA molecules that are found in the nuclei
What is mitosis?
The stage of the cell cycle where the cell divides
What do multicellular organisms use mitosis for?
To grow or replace cells that have been damaged
Describe each stage of mitosis
Prophase - The chromosomes shorten and duplicate
Metaphase - The chromosomes line up on the equator of the cell
Anaphase - The chromosomes are pulled to the opposite ends of the cell. The chromatids are now known as daughter cells.
Telophase - New membranes form around the daughter nuclei which becomes the nuclei of the two new cells - the nucleus has divided. The cytoplasm and cell membrane divide to create two daughter cells.
What are stem cells?
They are undifferentiated cells that divide to produce lots more undifferentiated cells. They then differentiate into different types of cell
Where are stem cells found?
In early human embryos or the bone marrow of adults
What do embryonic stem cells do?
Used to replace faulty cells in sick people - insulin-producing cells for diabetes and nerve cells for paralysed spinal injuries
Used to replace faulty blood cells
Where are stem cells found in plants?
Meristems
What is diffusion?
Diffusion is the movement of particles from an area of high concentration to an area of low concentration
Name the substances that can diffuse through cell membranes
Glucose, water, oxygen and amino acids
Name two substances that can't diffuse through cell membranes
Protein and starch
What is osmosis?
Osmosis is the passive movement of water molecules through a partially permeable cell membrane from an area of high water concentration to an area of low water concentration
What are the two main differences between active transport and diffusion?
Active transport uses energy whereas diffusion doesn't. Active transport goes against the concentration gradient whereas diffusion goes along it
Adaptations of Exchange Surfaces
Large surface area - lots of substances can diffuse at once
Lots of blood vessels - to get stuff into and out of the blood quickly
Thin membrane - short distance for substances to diffuse
Often ventilated - air moves in & out
Give two ways that the villi in the small intestine are adapted for absorbing digested food
A single layer of surface cells
A very good blood supply to assist quick absorption
Explain how the leaves are adapted to maximise the amount of carbon dioxide that gets into their cells
The exchange surface in a leaf is covered in stomata which the carbon dioxide diffuses through
The leaf has a flattened shape which increases the area of its exchange surface, therefore it's more effective
The walls of the cells inside the leaf act as another exchange surface
The air spaces inside the leaf increase the area of the exchange surface which increases the chance for carbon dioxide to enter the cells
What affects the rate of diffusion?
Concentration gradient - the steeper the gradient, the faster the rate
Temperature - the higher the temperature, the faster the rate (the particles have more energy thus move around faster)
Surface area - the larger it is, the faster the rate
Diffusion distance - the shorter the distance, the faster the rate
Examples of active transport
Plants = Root hairs absorb minerals and water. Each branch of a root will be covered in tiny hairs, therefore increasing the surface area for the absorption of minerals and water. The concentration of minerals is usually higher in the root hair cells than in the soil around them, therefore they can't use diffusion for this process.
Animals = Glucose is taken in from the gut and from kidney tubules.
How are alveoli in the lungs specialised to maximise the diffusion of oxygen and carbon dioxide?
-an enormous surface area
-a moist lining for dissolving gases
-very thin walls
-a good blood supply
How do fish respire?
-Water enters the fish through the mouth and passes out through the gills
-During this process, oxygen diffuses from the water into the blood in the gills and carbon dioxide diffuses from the blood into the water
How are fish adapted for gas exchange?
-Each gill is made up of lots of gill filaments which create a large surface area for the exchange of gases
-Gill filaments are covered in lamellae which increase the surface even more
-The lamellae have lots of blood capillaries to speed up diffusion
-The lamellae have a thin surface layer of cells to minimise the diffusion distance
-Blood flows through the lamellae one way and water flows over in the opposite direction which maintains a higher concentration gradient between the blood and the water
-The concentration of oxygen in the water is always higher than that in the blood to maximise the amount of oxygen diffusion from the water into the blood
Microscopy Practical - Preparing the Slide
Add a drop of water to the middle of a clean slide
Cut up an onion & separate it out into layers. Use tweezers to peel off some epidermal tissue from the bottom of one of the layers
Using the tweezers, place the epidermal tissue into the water on the slide
Add a drop of iodine solution - a stain used to highlight objects in a cell by adding colour to them
Place a cover slip on top - stand the cover slip upright on the slide, next to the water droplet. Then, carefully tilt & lower it so it covers the specimen. Try not to get any air bubbles under there - there'll obstruct your view
Microscopy Practical - Using a Light Microscope
Clip the slide you've prepared onto the stage
Select the lowest-powered objective lens
Use the coarse adjustment knob to move the stage up to just below the objective lens
Look down the eyepiece. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus
Adjust the focus with the fine adjustment knob, until you get a clear image of what's on the slide
Microscopy Practical - Drawing Observations
Draw what you see under the microscope using a pencil with a sharp point
Make sure your drawing takes up at least half of the space available & that it is drawn with clear, unbroken lines
Your drawing should not include any colouring or shading
If you are drawing cells, the subcellular structures should be drawn in proportion
Include a title & write down the magnification that it was observed under
Label the important features of your drawing using straight, uncrossed lines
What happens during binary fission?
The circular DNA & plasmid(s) replicate
The cell gets bigger & the circular DNA strands move to opposite poles of the cell
The cytoplasm begins to divide & new cell walls begin to form
The cytoplasm divides & two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmid(s)
What is binary fission?
A type of simple cell division used by prokaryotic cells to reproduce & split into two
What conditions do bacteria need to divide?
Warm environment
Lots of nutrients
What is the mean division time?
The average amount of time it takes for one bacterial cell to divide into two
How do you make an agar plate?
Hot agar jelly is poured into shallow Petri dishes. When the jelly's cooled & set, inoculating loops can be used to transfer the microorganisms to the culture medium. Alternatively, a sterile dropping pipette & spreader can be used to get an even covering of bacteria. The microorganisms then multiply
Investigating the Effect of Antibiotics on Bacterial Growth - Method
Place paper discs soaked in different types of antibiotics on an agar plate that has an even covering of bacteria. Leave some space between the discs
The antibiotic should diffuse into the agar jelly. Antibiotic-resistant bacteria that aren't affected by the antibiotic will continue to grow on the agar around the paper discs, but non-resistant strains will die. A clear area will be left where the bacteria have died - an inhibition zone
Make sure you use a control - a paper disc that has not been soaked in an antibiotic. Instead, soak it in sterile water so you can be sure that any difference between the growth of bacteria around the control disc & around one of the antibiotic discs is due to the effect of the antibiotic alone
Leave the plate for 48 hours at 25°C
Note 
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