Topic 1 - Key concepts in biology

Question 1

What is the function of the nucleus?

Answer 1

It contains DNA which codes for enzymes and other proteins and coordinates cell activity

This is in eukaryotic and prokaryotic cells (bacteria + plant + animal)

Question 2

What is the function of the cytoplasm?

Answer 2

-A jelly-like substance which chemical reactions occur in

This is in all eukaryotic cells (plant + animal)

Question 3

What is the function of the cell membrane?

Answer 3

-It controls what exits and enters the cell

This is in prokaryotic and eukaryotic cells (bacteria + plant + animal)

Question 4

What is the function of mitochondria?

Answer 4

-It contains the enzymes for respiration, providing energy for the cell
This is in all eukaryotic cells (plant + animal)

Question 5

What is the function of ribosomes?

Answer 5

-Where protein synthesis occurs (proteins are made)

This is in prokaryotic and eukaryotic cells (bacteria + plant + animal)

Question 6

What is the function of chloroplasts?

Answer 6

-It contains the green pigment, chlorophyll, which absorbs light energy for photosynthesis
-It contains the enzymes needed for photosynthesis

This is only in plant cells

Question 7

What is the function of the vacuole?

Answer 7

-It contains cell sap
-Supports the cell/improves its rigidity

This is only in plant cells

Question 8

What is the function of the cell wall?

Answer 8

-Made of cellulose
-Provides structure

This is in plant cells, some bacteria have them

Question 9

What is the function of plasmids?

Answer 9

Small loops of DNA which control a few of the cell’s activities

Question 9

What is the function of chromosomal DNA?

Answer 9

It is one singular loose loop of DNA which controls most of the cell’s activities

Question 10

What is the function of the flagella?

Answer 10

Propels the bacteria to allow movement

Question 11

How are sperm cells adapted to their function?

Answer 11

Their function as a gamete is to carry the male’s DNA to the egg cell for successful reproduction

-Contain an acrosome, which contains enzymes which, when released, breaks down the outer layers of the egg cell’s membrane
-Has a haploid nucleus, has 23 chromosomes as an egg cell has the other 23
-Has a streamlined head to aid swimming
-Has a tail for swimming
-Contains many spiralled mitochondria, because it needs to respire to move, this supplies the energy and the spiral is more compact

Question 11

How are egg cells adapted to their function?

Answer 11

-Has a haploid nucleus, has 23 chromosomes as a sperm cell has the other 23
-Has a special cell membrane which becomes impermeable after accepting one cell
-Cytoplasm contains nutrients for the growth of the early embryo

Question 12

How are ciliated epithelial cells adapted to their function?

Answer 12

-It has a thin layer of long hair-like projections called cilia that waft mucus that contains trapped microbes from one place to another, eventually to be transported to the stomach and kill by stomach acid.

Question 13

Explain the advantage of electron microscopes

Answer 13

Electron microscopes have a greater magnification and resolution than light microscopes. They can have a magnification of up to 2,000,000x and resolving power of 10nm.

This means they can view things such as organelles, viruses or proteins more clearly and in more detail, especially very small structures. These can be identified more easily

Question 14

What is the equation for the total magnification of a light microscope?

Answer 14

magnification of the eyepiece lens x magnification of the objective lens

Question 15

What is the equation for the size of an object?

Answer 15

size of image/magnification = size of object

Question 16

Name each quantitive unit, their symbol how they are expressed in standard form

Answer 16

milli (10⎺³) 0.001 mm
micro (10⎺⁶) 0.000001 µ
nano (10⎺⁹) 0.000000001 n
pico (10⎺¹²) 0.000000000001 p

Question 17

Describe how you prepare a slide for the core practical investigating biological specimens using a microscope

Answer 17

-Take a thin layer of cells from your sample by peeling them off or using a cotton bud
-Add a small amount of chemical stain, this makes some parts of the specimen more visible through the microscope
-Apply the cells to your glass side by placing them/wiping the bud against
-Lower a coverslip onto your slide, taking care to avoid air bubbles

Question 18

Describe how to investigate biological specimens using a microscope

Answer 18

-Place the slide on the stage and clip with stage clips
-Look through the eyepiece lens -Turn the focus wheel to obtain a clear image
-Start with the lowest objective lens magnification
-Increase the magnification of the objective lens and refocus using the fine focus adjustment

Question 18

Explain the mechanism of enzyme action

Answer 18

In the Lock and Key Hypothesis the shape of the substrate is complementary to the shape of the active site, so when they bond it forms an enzyme-substrate complex

Question 19

Explain the effect of temperature on enzyme activity

Answer 19

The rate of reaction increase with an increase in temperature up to the optimum, but above this temperature it rapidly decreases and eventually the reaction stops.
When the temperature becomes too hot the bonds that hold the enzyme together will begin to break.
This changes the shape of the active site, so the substrate can no longer fit the enzyme, which is now denatured and cannot work.

Question 20

Explain the effect of substrate concentration on enzyme activity

Answer 20

As the substrate concentration increases, the rate at which enzyme-substrate complexes can be formed increases.
This only occurs up to a point, however - this is called the saturation point, and increasing the substrate concentration above this will have no effect on the rate of reaction.
The saturation point is different for every enzyme.

Question 21

Explain the effect of pH on enzyme activity

Answer 21

Enzyme activity and the rate of reaction is highest at the optimum pH.

If the pH is too high or too low, the forces that hold the amino acid chains that make up the protein will be affected.
This will change the shape of the active site so the substrate can no longer fit in: the enzyme is denatured and can no longer work.

Question 21

Describe the core practical to investigate the effect of pH on enzyme activity

Answer 21

-Place single drops of iodine solution on each well of a tray -Label a test tube with the pH to be tested. Place it in a water beaker and place this above a Bunsen burner for 3 minutes (to keep the pH at a constant temperature) -Place amylase solution, starch solution and pH solution in a test tube and start a stopwatch. -After 10 seconds, use a pipette to place a drop of the solution into into one of the wells containing iodine solution. The mixture should turn blue-black to indicate that starch is present and hasn't been broken down. -Repeat this every 10 seconds until the solution remains orange and record the time taken. -Repeat with solutions of different pHs -Record results on a graph of pH (on the x-axis) and time taken to complete reaction (on the y-axis).

Question 21

Explain how the core practical to investigate the effect of pH on enzyme activity works.

Answer 21

Amylase breaks down carbohydrates such as starch into simple sugars. We can use iodine to check for the presence of starch in the solution. When starch is present it will be blue-black, and orange when it isn't. This experiment estimates amylase's optimum pH - which is around pH 7.

Question 22

What is the calculation for rate of reaction?

Answer 22

Rate = change/time

Question 23

Explain the importance of enzymes in different types of synthesis

Answer 23

Enzymes are biological catalysts: -in the synthesis of carbohydrates into simple sugars -in the synthesis of proteins into amino acids -in the synthesis of lipids into fatty acids and glycerol

Question 24

Describe the iodine test

Answer 24

-Place a spatula of the food sample on a dish. -Using a dropper, place a few drops of iodine solution onto the food -If starch is present, the colour will change from orange to blue-black

Question 25

Describe the Benedict's solution test

Answer 25

-Place 2 spatulas of the food sample into a test tube and add 1cm³ water to the tube and stir. -Add an equal volume of Benedict's solution and mix -Place the tube in a water bath at about 95℃ for a few minutes -If reducing sugars are present then the solution will gradually turn from blue to a brick red.

Question 26

Describe the Biuret test

Answer 26

-Place one spatula of the food sample into a test tube. Add 1cm³ water to the tube and stir to mix. -Add an equal volume of potassium hydroxide solution to the tube and stir. -Add two drops of copper sulfate solution and stir -If protein is present then it will turn from blue to purple

Question 27

Describe the Emulsion test

Answer 27

-Place 2 spatulas of the food sample into a test tube. -Add 2cm³ of ethanol to the tube. Cover the end of the tube and shake it vigorously. -Allow the contents to settle -Pour the liquid from the top of the mixture into a test tube half-filled with water -Record whether the water is cloudy or clear -If lipids are present, there will be a white emulsion layer at the top of the sample

Question 28

Explain how the energy contained in food can be measured using calorimetry

Answer 28

This energy is measured in calories. A simple calorimeter: -Take a tube of 50ml cold water -Record the starting temperature -Heat the test tube to 45 degrees and hold a burning food sample just beneath it. -When the food is burned up, record the final temperature of the water -Use the increase in temperature of water to calculate the energy content

Question 29

What is the equation for energy transferred for calorimetry?

Answer 29

Energy transferred = mass of water x 4.2 (specific heat capacity of water) x temperature increase

Question 30

Explain the features a calorimeter has to make it effective

Answer 30

The lid reduces heat loss so energy from sugar is used to heat water and the result is more accurate. Stirring the water ensures heat is distributed evenly throughout the water.

Question 31

Describe diffusion

Answer 31

A form of passive transport (doesn't require energy). Although particles move in both directions the next movement is from a high to a low concentration.

Question 32

Describe osmosis

Answer 32

It's a form of passive transport that only applies to water. It is the movement of water molecules from an area of high solute concentration to an area of low solute concentration across a partially permeable membrane.

Question 33

Describe Active Transport

Answer 33

It is a form of transport that does require energy. It moves molecules against a concentration gradient, from a low concentration to a high concentration.

Question 34

Describe the core practical to investigate osmosis in potatoes

Answer 34

-Cut potato into small discs of equal size -Blot the potato discs gently with tissue paper to remove excess water -Measure the initial mass of each disk -Place the discs in sucrose solutions of different concentrations -Blot with tissue paper again and record new mass -Find the difference in mass and use the percentage change to calculate percentage gain or loss of mass Water should move by osmosis from where it is highly concentrated to where it is less highly concentrated

Question 35

What is the equation for percentage change?

Answer 35

Change in mass/starting mass x 100