Section 1- Key Concepts In Biology

Question 1

What are specialised cells

Answer 1

Cells that have a structure which makes them adapted to their function

Question 2

What cells are specialised for reproduction

Answer 2

• Egg cells
• Sperm cell

Question 3

What happens in sexual reproduction

Answer 3

The nucleus of an egg fuses with the nucleus of a sperm cell to create a fertilised egg which develops into an embryo. Both the nucleus and the egg contain half of the number of the chromosomes (23) which makes then haploid.
This is important as it means that when the egg and sperm combine at fertilisation the resulting cell will have the right amount of chromosomes - 46 making it diploid

Question 4

Function of an egg cell and how it is adapted to the function

Answer 4

1. To Carry the female DNA
2. Nourish the developing embryo in early stages
3. Cytoplasm contains the nutrients to feed the embryo
4. It has a Haploid nucleus
5. Membrane changes structure after fertilisation to stop any more sperm getting in. This is to make sure the offspring ends up with the right amount of DNA.

Question 5

Function of sperm cell and how it’s adapted

Answer 5

Function of sperm cell is to transport a makes DNA to the females egg.
1. Long tale so it can swim to the egg
2. Contains mitochondria in the middle section to provide energy from respiration needed to swim the distance
3. Haploid nucleus
4. Acrosome infront of the head where it stores enzymes needed to digest its way through the membrane of the egg cell.

Question 6

What are ciliated epithelial cells

Answer 6

They are cells specialised for moving materials.
1. Line the surface if organs
2. Some of them have cilia (hair like structures) on the top surface of the cell.
3. Function is to move substances, the cilia beat to move substances in one direction along the surface of the tissue
4. Example, the lining of the airways contains lots of ciliated epithelial cells which helps to move mucus and all the particles from the air that it has trapped up to the throat so it can be swallowed and doesn’t reach the lungs.

Question 7

Microscopes

Answer 7

Cells are studied through microscopes. Microscopes uses lenses to magnify images, they also increase the resolution of an image.

Question 8

Resolution

Answer 8

How well a microscope distinguishes between two points that are close together

Question 9

Magnification

Answer 9

the ability to make small objects seem larger

Question 10

Light microscopes

Answer 10

• Invented in 1590
• Works by passing light through the specimen and they let us see things like nuclei and chloroplasts and we can also use them to study living cells

Question 11

Electron microscopes

Answer 11

• Invented in 1930
• Uses electrons rather than light
• Have higher magnification and resolution than light microscopes so they let us see smaller things in more detail like the internal structure of the mitochondria and chloroplast
• Allows us to have more greater understanding of how cells work in the role of sub cellular structures
  -They can’t be used to view living cells

Question 12

How to view specimen using a light microscope (PRACTICAL)

Answer 12

1) You need a thin slice of the specimen in order for light to get through it
2) Get a clean slide and use a pipette to put one drop of water in the middle of the thin slice, this will secure the specimen in place
3) Use tweezers to place your specimen on the slide
4) if the specimen is completely transparent or Colourless had a drop of Stain this will make the specimen easy to see. (However different stains highlight different structures within the cell for example methylene blue stains DNA)
5) place a cover slip at one end of a specimen and hold it as an angle with a mounted needle and carefully lower it on to the slide
6) place the coverslip gently so that no air bubbles are trapped underneath it, then clip the slide onto the stage
7) select the lowest power objective lens on the microscope
8) use the course adjustment knob to move the stage up so that the slide is just underneath objective lens
9) you look down into the eyepiece and move the stage downwards so you don’t accidentally crash it into the lens, do this until the specimen is nearly in focus
10) adjust the focus with the fine adjustment knob until you get a clear image
11) Position a clear ruler on the stage and use it to measure the diameter of the circular area visible- field of view
12) if you need to see a specimen with greater magnification swap to a higher power objective lens, refocus and re-calculate your field of view

Question 13

How to create a scientific drawing of specimen (PRACTICAL)

Answer 13

1) use a sharp pencil,and draw outlines of the main features using clear, unbroken lines. Don’t included colouring or shading
2) drawing has to take half of the space available and remember to keep all the parts in proportion
3) Label the important features with straight lines which don’t cross over and include the magnification used and a scale

Question 14

How to workout Total Magnification

Answer 14

Total Magnification = eyepiece lens magnification x objective lens magnification

Question 15

How to workout magnification if you don’t know which lenses were used

Answer 15

Magnification = Image size/real size
(Both measurements of the image size and the real size should have the same units, if they don’t you need to rearrange the equation using the formula triangle)

     Image size Real size   X magnification

Question 16

What are enzymes

Answer 16

• Biological catalysts produced by living things
• Reduce the need for high temperatures
• Only use enzymes to speed up the useful chemical reactions
• they also break down big molecules

Question 17

How can we make a reaction happen quickly

Answer 17

Raising the temperature speeds up reactions, however it also speeds up unwanted reactions as well as wanted reactions

Question 18

What do enzymes have to catalyse reactions

Answer 18

• Enzymes have special shapes so they can catalyse reactions
  1. Substrate- the molecule changed in the reaction
  2. Active site- the part wheee it joins onto the substrate to catalyse the reaction

Question 19

What is the ‘lock and key’ mechanism

Answer 19

Enzymes can only work with one substrate. They are said to have high specificity for their substrate. This is because for the enzyme to work, the substrate has to fit into the active site. If the substrates shape doesn’t match the active sites shape, then the reaction won’t be catalysed.

Question 20

Why is it called the lock and key mechanism

Answer 20

As the substrate fits into the enzyme just like a key fits into a lock

Question 21

What affects the rate of reaction

Answer 21

• pH
• Temperature
• Substrate concentration

Question 22

How does temperature affect the rate of reaction

Answer 22

• a higher temperature increases the rate at first, but if it gets too hot, some of the bonds holding the enzyme together breaks.
• once the bond breaks the shape of the enzymes active site changes so the substrate won’t fit anymore. This means it has ‘denatured’
• all enzymes have an optimum temperature that they work best at

Question 23

What does denature mean

Answer 23

When the enzymes active site changes shape so the substrate doesn’t fit anymore

Question 24

How does the pH affect the rate of reaction

Answer 24

• the ph interferes with the bonds holding the enzyme together which changes the shape of the active site and the enzyme becomes denatured
• all enzymes have an optimum pH which is often - neutral pH 7. But not always

Question 25

What pH does pepsin work best at

Answer 25

Pepsin is an enzyme which breaks down proteins in the stomach. So this means it works best at pH 2, so it is well suited in more acidic conditions

Question 26

How does the substrate condition affect the rate of reaction

Answer 26

• the higher the substrate condition, the fasted the reaction. This is because it is more likely that the enzyme will meet up and react with a substrate molecule
• this is only true until up to a point. After that, there are so many substrate molecules so the enzymes have about as much as possible where they can cope so all the active sites are full. Adding more substrates makes no difference

Question 27

How to detect starch

Answer 27

The enzyme amylase catalyses the breakdown of starch and maltose. It is easy to detect starch using iodine solution- if starch is present, the iodine solution will change from browny-orange to blue-black.

Question 28

How to investigate the Effect of pH on Enzyme activity (PRACTICAL)

Answer 28

1. Put a drop of iodine solution into every tile on the spotting tile.
2. Place a Bunsen burner on the heat proof mat, a tripod and a gauze over the Bunsen burner
3. Put a beaker of water on top of a tripod and heat the water until it’s 35°C. (Use a thermometer to measure the temperature) tried to keep the temperature of the water constant throughout the whole experiment.
4. Use a syringe to add a 30 cm³ of amylase solution and 1 cm³ of buffer solution with a pH of 5 to a boiling tube.
5. Put the boiling tube into the beaker of water and wait for five minutes.
6. Use a different syringe to add 3 cm³ of starch solution to the boiling tube
7. Immediately mix the contents Of the boiling tube and start a stop clock.
8. Use continuous sampling to record how long it takes for the amylase breakdown starch. Do do this use a dropping pipette to take a fresh sample from the boiling tube and every 10 seconds put a drop into a tile. If the iodine solution remains brown orange starch is no longer present.
9. Repeat the whole experiment with buffer solutions of different pH to see how pH affects the time taken for starch to be broken down
10. Control any variables each time to make it a fair test

Question 29

How to make ‘investigate the effect of pH on enzyme activity’ a fair test

Answer 29

Control and variables each time, like concentration and volume of amylase solution

Question 30

What else can you use instead of a Bunsen burner and a beaker to control the temperature of the water

Answer 30

Am electric water bath

Question 31

How to accurately measure the pH of solutions

Answer 31

A pH meter

Question 32

How to calculate the rate of reaction

Answer 32

Rate = 1000/time
Units are s^-1

Question 33

Why is it important that organisms are able to break down big molecules into smaller components in the body

Answer 33

So they can be used for growth and other life processes
- many of the molecules in the food we eat are too big to pass through the walls of our digestive system, so the digestive enzymes break them down into smaller, soluble molecules. These can pass easily through the walls of the digestive system, allowing them to be absorbed into the bloodstream. They can be passed into cells and to be used by the body.

Question 34

Why is it important that organisms are able to break down big molecules into smaller components in plants

Answer 34

• Plants store energy in the form of starch (carbohydrate). When plants need energy, enzymes break down the starch into smaller molecules (sugars) these can be used for respiration to transfer energy to be used by the cells

Question 35

Why can’t yeast cells produce glucose

Answer 35

They don’t have chloroplasts so they don’t contain chlorophyll so they can’t photosynthesise

Question 36

How to convert mm to μm

Answer 36

mm - μm = x100

μm - mm = divide 100

Question 37

Millimetre in standard form

Answer 37

X 10^-3m

Question 38

Micrometer in standard form

Answer 38

X 10^-6m

Question 39

Nanometer in standard form

Answer 39

X 10^-9

Question 40

Picometer in standard form

Answer 40

X 10^-12m