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Name the two types of cells
Prokaryotic and Eukaryotic
What is a prokaryotic cell?
A cell without a nucleus
Give an example of a prokaryote (Prokaryotic cell)
Bacteria
What is a eukaryotic cell?
cell with a nucleus
Give two examples of eukaryotic cells
Plant & Animal cells
What three sub-cellular structures do plant cells have which animal cells do not?
Permanent vacuole, cell wall and chloroplasts
What is the function of the nucleus?
Contains genetic materials that controls the activities of the cell
What is the function of the cytoplasm?
A gel-like substance where most of the chemical reactions happen. It contains enzymes that control these reactions
What is the function of the cell membrane?
Holds the cell together and controls the passage of substances (controls what goes in and out)
What is the function of the mitochondria?
These are where most of the reactions for aerobic respiration take place. Respiration transfers energy that the cell needs to work
What is the function of the ribosome?
These are were proteins are made in the cell through protein synthesis
What is the function of the cell wall and what is it made of ?
To strengthen and support the cell
Made of cellulose
What is the function of the vacuole?
Contains cell sap (a weak solution of sugar and salts), it keeps the cell turgid
What is the function of the chloroplast?
This is where photosynthesis takes place, which makes food for the plant. They contain a green substance called chlorophyll which absorbs the light required for photosynthesis
What do bacterial cells have instead of a nucleus?
A single circular strand of DNA that floats freely in the cytoplasm, and some may also contain one or more small rings of DNA called plasmids.
How many mm are in um?
1000
What do light microscopes use to work?
Light and lenses to form an image of a specimen. They let us see individual cells and large sub cellular structures such as nuclei
What is the formula triangle for magnification?
Magnification=Image size/real size
What do electron microscopes use to work?
Electrons instead of light to form an image. They have a much higher magnification than light microscopes
How are electron microscopes better than light microscopes?
They allow us to see much smaller things in greater detail since they have a higher magnification and resolutions. For example, using an electron microscope, we can see the internal structure of mitochondria and chloroplast
Describe the steps to prepare a slide [Required Practical]
Add a drop of water to the middle of a clean slide
Cut up an onion and separate it out into layers. Use tweezers to peel off some epidermal tissue from the bottom of one the layers
Using the tweezers, place the epidermal tissue into the water on the slide
Add a drop of iodine solution. Iodine solution is a stain which is used to highlight objects in the cell by adding colour to them
Place a cover slip on top. To do this, stand the cover slip upright on the slide, next to the water droplet. Then carefully tilt and lower it so it covers the specimen. Try not to get any air bubbles underneath it - they'll obstruct your view of the specimen
Describe the steps needed to use a light microscope to look at your slide [Required Practical]
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
If you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocus
What is cell differentiation?
Cell differentiation is the process by which a cell changes to become specialised for its job.
What is cell specialisation?
The process of cells as they develop depending on their location in a tissue or organ.
What is a stem cell?
A type of undifferentiated which are able to become any type of cell
How are sperm cells specialised?
For reproduction: they have a long tail and a streamlined head to help it swim to the egg,
There are lots of mitochondria in the cell to provide the energy needed
It also carries enzymes in its head to digest through the egg cell membrane
How are nerve cells specialised?
For rapid signalling: these cells are long to cover more distances and have branched connections at their ends to connect to other nerve cells and form a network throughout the body
How are muscle cells specialised?
For contraction: these cells are long so that they have space to contract and have lots of mitochondria to generate the energy needed for contraction
How are root hair cells specialised?
For absorbing water and minerals: they grow into long "hairs" that stick out into the soil. This gives the plant a large surface area for absorbing water and mineral ions from the soil
How are phloem and xylem cells specialised?
For transporting substances: phloem cells form phloem tubes and xylem cells form xylem tubes which transport substances such as food and water around plants - the cells are joined end to end.
Xylem cells are hollow in the centre and phloem cells have few sub cellular structures, so that stuff can flow through them
Define the term chromosome
Coiled up lengths of DNA molecules, they contain your genetic information
How many pairs of chromosomes are there in humans?
23
What is the purpose of mitosis in multicellular organisms?
For growth, development and repair
What is the end result of mitosis?
2 identical daughter cells
Where are stem cells found in the human body?
Early human embryos, bone marrow and umbilical cords
What can stem cells from embryos and bone marrow do?
Produce clones and made to differentiate into specialised cells to use in medicine or research
How can stem cells cure diseases?
By replacing faulty cells
You could make insulin-producing cells for people with diabetes or nerve cells for people paralysed by spinal injuries
What is the name for the type of cloning that gives the offspring the identical genetic informations as the patient?
Therapeutic cloning
Why are some people against stem cell research?
They feel that human embryos shouldn't be used for experiments since each one is a potential human life
Where can stem cells be found in plants?
Meristems
Why is producing identical plants important?
Rare species can be cloned (this prevents them from being wiped out), farmers can use them to grow identical crops with a desired characteristic, for example disease resistance.
Define diffusion
The movement of particles from an area of high concentration to an area of low concentration
What factors effect effect the rate of diffusion?
The size of the concentration gradient (the bigger the gradient, the faster the rate)
The temperature (the higher the temperature, the faster the rate)
Define osmosis
The movement of water molecules from an area of high concentration to an area of low concentration across a partially permeable membrane
What is meant by a partially permeable membrane?
A membrane with very small holes in it, which allows tiny molecules to pass through
Describe the steps to observe the effect of sugar solutions on plant tissue [Required Practical]
Cut up a potato into identical cylinders and get some beakers with different sugar solutions in them. One should be pure water and another should be a very concentrated sugar solution. Then you can have a few other with concentrations in between
Measure the mass of the potato cylinders, then leave one in each beaker for 24 hours
Then take them out, dry with a paper towel to remove any access water/solution and measure the masses again
If the potatoes have drawn in water by osmosis, they'll have an increase in mass. If water has been drawn out, they'll have a decrease in mass
The dependant variable is the chip mass and the independent variable is the concentration of the sugar solution
To reduce the effect of errors (e.g. from the potato cylinders not being fully dried or water being evaporated) complete the experiment three times and calculate the mean percentage change at each concentration
Why do we calculate the percentage of the mass of the potatoes?
So you can compare the effect of sugar concentration on potato cylinders that didn’t have the same starting mass
Define active transport
The movement of water and ions from an area of low concentration to and area of high concentration against the concentration gradient
Energy is required
What cells use active transport to move minerals and water?
Root hair cells
How does the plant get energy for active transport?
Through respiration
Where does active transport occur in humans and why?
Active transport is used in the gut when there is a lower concentration of nutrients in the gut, but a higher concentration of nutrients in the blood
Give an example of how exchange surfaces are used in the human body
When oxygen and carbon dioxide are transferred between cells and the environment during gas exchange
What factor effects how easy an organism exchanges substances?
Surface area to volume ratio
How can you work out the surface area to volume ratio?
By working out the total surface area using the equation: length x width, and by working out the volume using the equation: length x width x height, then put your answer into the ratio x:y (with x being the surface area and y being the volume)
Why do multicellular organisms need exchange surfaces?
To allow the necessary amount of substances to pass through
Why do single-celled organisms need exchange surfaces?
So that enough substances can be exchanged across the membrane to supply to volume of the cell
How are exchange surfaces adapted to maximise effectiveness?
By having a thin membrane, so substances only have a short distance to diffuse
By having a large surface area so lots of a substance can diffuse at one
Exchange surfaces in animals have lots of blood vessels, to get stuff into and out of the blood quickly
Gas exchange surfaces in animals (e.g. alveoli) are often ventilated to let the air move in and out
What is the function of lungs?
To transfer oxygen to the blood and remove waste carbon dioxide
How do the lungs complete gas exchange?
By containing millions of little air sacs called alveoli where gas exchange takes place
How have the alveoli been specialised to maximise diffusion?
They have an enormous surface area (about 75m2 in humans)
A moist lining for dissolving gasses
Very thin walls and have a good blood supply
What do the villi provide?
A really big surface area
Where are villi found?
Small intestine
Why do the villi increase the surface area?
So that digested food is absorbed much more quickly into the blood
What do villi have?
A single layer of surface cells
A very good blood supply to assist quick absorption
What is the stomata and what is it's function?
Openings in the leaves of plants, particularly on the underside, they open and close by guard cells, allowing gasses to enter and leave the leaf
What is the shape of a leaf and why is it shaped this way?
It has a flattened shape to increase the area of the exchange surface so that it is more effective
What is the function of gills?
Gas exchange in fish
What do gills have to help gas exchange?
A large surface area
How do the gills use gas exchange?
Water (containing oxygen) enters the fish through its mouth and passes through the gills
As this happens, oxygen diffuses from the water into the blood into the gills and carbon dioxide diffuses from the blood into the water
They also have a thin surface layer of cells to minimise the distance in which the gases have to diffuse.
What are tissues?
A group of similar cells that work together to carry out a particular function
What are organs?
An organ is a group of different tissues that work together to perform a particular function
What is an organ system?
A group of organs working together to perform a particular function
Name three examples of tissues and their function in mammals
Muscular Tissue: contracts to move whatever it's attached to
Glandular Tissue: makes and secretes chemicals like enzymes and hormones
Epithelial Tissue: covers some parts of body (e.g. inside the gut)
Name the three tissues and their function in the stomach
Muscular Tissue: moves the stomach wall to churn up the food
Glandular Tissue: makes digestive juices to digest food
Epithelial Tissue: covers the outside and inside of the stomach
Name five examples of organs and their function in the organ system
Glands: (e.g. pancreas and salivary glands) which produce digestive juices
The stomach: digests food
The liver: produces bile
The small intestine: absorbs soluble food molecules and helps digest food
The large intestine: absorbs water and undigested food, leaving faeces
What is an enzyme?
A biological catalyst
What is a catalyst?
A catalyst is a substance which increases the speed of a reaction, without being changed or used up in the reaction
What are enzymes made up of?
Enzymes are all large proteins, and all proteins are made up of chains of amino acids
What is an active site?
A region on an enzyme with a unique shape that binds onto the substrate involved in a reaction
What is the lock and key model?
Enzymes are specific to the substrate they bind too.
What happens to the enzyme if the temperature exceeds the optimum temperature for the enzyme?
The enzyme begins to denature, meaning it will no longer work
What happens to the enzyme if the pH exceeds the optimum pH for the enzyme?
The enzyme begins to denature, meaning it will no longer work
What is the optimum temperature for enzymes?
37 degrees
What is the optimum pH for enzymes?
7
What is the optimum pH for the enzyme pepsin? (used to break down proteins)
2
Describe the steps to investigate the effect of pH on enzyme activity [Required Practical]
Put a drop of iodine solution into every well of a spotting tile
Place a Bunsen burner on a heat-proof mat, and a tripod and gauze over the Bunsen burner. Put a beaker of water on top of the tripod and head the water until it is 35 degrees. Try to keep the temperature of the water constant throughout the experiment
Use a syringe to add 1cm3 of amylase solution and 1cm3 of buffer solution with a pH of 5 to a boiling tube. Using test tube holder, put the tube into a beaker of water and wait for five minutes.
Next, use a different syringe to add 5cm3 of starch solution to the boiling tube
Immediately mix the contents of the boiling tube and start a stop clock
Use continuous sampling to record how long it takes for the amylase to break down all of the starch. To do this, use a dropping pipette to take a fresh sample from the boiling tube every 30 seconds and put a drop into a well. When the iodine solution remains browny-orange, starch is no longer present
Repeat the whole experiment with buffer solutions of different pH values to see how pH affects the time taking for the starch to be broken down.
Remember to control any variables each time to make it a fair test
What does denaturing mean?
Some of the bonds holding the enzyme together break.
This changes the shape of the active site so the substrate won’t fit anymore
What is the equation to calculate the rate of reaction?
Rate = 1000/time
What do digestive enzymes do?
They break down big molecules into smaller ones
What does the enzyme amylase do?
breaks down starch into maltose
What is amylase an example of?
Carbohydrase
Where is amylase made?
Salivary glands
Pancreas
Small intestine
What does the enzyme protease do?
Convert proteins into amino acids
Where is protease made?
Stomach (it is called pepsin there)
Pancreas
Small intestine
What does the enzyme lipase do?
Convert lipids into glycerol and fatty acids
Where is lipase made?
Pancreas
Small intestine
What is the function of bile?
It emulsifies fats
Neutralises the stomach acid
Define emulsification
The breakdown of fat into tiny droplets to give as much surface area of fat for the enzyme lipase to work on
What are enzymes produced by?
Specialised cells in glands and in the gut lining
What is the function of the salivary glands?
To produce amylase enzymes in the saliva
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