AQA GCSE Combined Science Trilogy : Biology Paper 1

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

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?

To strengthen and support the cell

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?

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]

1) Add a drop of water to the middle of a clean slide
2) 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
3)Using the tweezers, place the epidermal tisse into the water on the slide
4) 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
5) 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]

1) Clip the slide you've prepared onto the stage
2) Select the lowest-powered objective lens
3) Use the coarse adjustment knob to move the stage up to just below the objective lens
4) Look down the eyepiece. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus.
5) Adjust the focus with the fine adjustment knob, until you get a clear image of what's on the slide
6) 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 and 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 mitosis?

Part of the cell cycle where one set of new chromosomes is pulled to each end of the cell forming two identical nuclei during cell division

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

What are stages of growth and DNA replication during mitosis?

1) In a cell that's not dividing, the DNA is all spread out in long strings
2) Before it divides, the cell has to grow and increase the amount of sub cellular structures such as mitochondria and ribosomes
3) It then duplicates its DNA - so there's one copy for each new cell. The DNA is coped and forms X-shaped chromosomes. Each 'arm' of the chromosome is an exact duplicate of the other.

What are the stages of mitosis?

Once its contents and DNA have been copied, the cell is ready for mitosis:
4) The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell
5) Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells - the nucleus has divided
6) Lastly, the cytoplasm and cell membrane divide: the cell has now produced two new daughter cells. The daughter cells contain exactly the same DNA - they're identical. Their DNA is also identical to the parent cell

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 (e.g. faulty blood cells), by making insulin-producing cells for people with diabetes, 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?

Meristem

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 with the concentration gradient

What factors effect effect the rate of diffusion?

The size of the concentration gradient (the bigger the gradient, the faster the rate) and 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 with the concentration gradient 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]

1) 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
2) Measure the mass of the potato cylinders, then leave one in each beaker for 24 hours
3) Then take them out, dry with a paper towel to remove any access water/solution and measure the masses again
4) 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
5) The dependant variable is the chip mass and the independent variable is the concentration of the sugar solution
6) 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 chips?

For control

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

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 and gas exchange surfaces in animals (e.g. alveoli) are often ventilated to let the air move in and out

Annotate the diagram of the lungs

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 the diffusion?

They have an enormous surface area (about 75m^2 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 and 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 this exchange surface so that it is more effective

What is the function of gills?

Gas exchange

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?

Groups of cells that are similar in structure and 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

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 speedo f 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

Why do enzymes have to fit the substrate exactly?

because they have a complex shape and can only fit to one specific substrate

What is an active site?

A region on an enzyme that binds to a protein or other substance during 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]

1) Put a drop of iodine solution into every well of a spotting tile
2) 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
3) Use a syringe to add 1cm^3 of amylase solution and 1cm^3 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.
4) Next, use a different syringe to add 5cm^3 of starch solution to the boiling tube
5) Immediately mix the contents of the boiling tube and start a stop clock
6) 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
7) 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.
8) Remember to control any variables each time to make it a fair test

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, pancreas, small intestine

What does the enzyme lipase do?

Convert lipids into glycerol and fatty acids

Where is lipase made?

Pancreas and small intestine