Topic 1 - Key Concepts

Question 1

What are Ribosomes?

Answer 1

Tiny structures where protein synthesis occurs to create proteins.

Question 2

What are electron microscopes?

Answer 2

They use electrons rather than light. Have a higher magnification and resolution so they let us see much smaller things in more detail like the internal structure of mitochondria and chloroplasts which has allowed a much greater understanding of how cells work and the role of sub cellular structures.

Question 3

Describe the Benedict’s test for reducing sugars. (6)

Answer 3

1) Place two spatulas of the food sample into a test tube or 1 cm3 if the sample is liquid. Add about 1 cm3 depth of water to the tube and stir to mix.
2) Add an equal volume of Benedict’s solution and mix.
3) Place the tube in a water bath at about 95°C for a few minutes.
4) Record the colour of the solution.
It turns from blue to green to yellow to orange to brick red. The higher the concentration of reducing sugar, the further along the colour change goes.

Question 4

How is the egg cell adapted to its function? (3)

Answer 4

Contains nutrients in the cyptoplasm to feed the embryo
Has a haploid nucleus
It membrane changes the structure to stop any more sperm getting in so that the offspring ends up with the right amount of DNA

Question 5

What is plasmid DNA?

Answer 5

Bacteria also have small, closed-circles of DNA called plasmids present in their cytoplasm. Unlike the chromosomal DNA, plasmid DNA can move from one bacterium to another giving variation.

Question 6

Why do enzymes have a high specifity for their enzyme?

Answer 6

This is because, fr the enzyme to work, the substrate has to fit into the active site. If the substrate’s shape doesn’t match the active site’s shape, then the reaction won’t be catalysed. This is called the ‘lock and key’ mechanism because the substrate fit into the active site like a key fits in a lock.

Question 7

What is the difference between eukaryotic and prokaryotic?

Answer 7

Eukaryotic cells are complex and include all animal and plant cells. Prokaryotic cells are smaller and simpler such as bacteria cells.

Question 8

How does a high/low pH affect an enzyme?

Answer 8

This also interferes with the bonds holding the enzyme together. This changes the shape of the active site and denatures the enzyme. All enzymes have an optimum pH which they work best at which is usually pH 7 but not always.

Question 9

How do you work out magnification?

Answer 9

Image size/ real size

Question 10

What is chromosomal DNA?

Answer 10

The DNA of bacterial cells is found loose in the cytoplasm. It is called chromosomal DNA and is not contained within a nucleus.

Question 11

What is an active site?

Answer 11

Every enzyme has an active site. It is the part where it joins on to its substrate to catalyse the reaction.

Question 12

Which three factors affect the rate of reaction in enzymes?

Answer 12

• Substrate concentration
• pH
• Temperature

Question 13

How do you work out rate?

Answer 13

1000/time(secs)= Rate (S^-1)

Question 14

Describe the relationship between millimetre, micrometre, nanometre and picometre.

Answer 14

A millimetre = 1000 micrometers
A micrometer = 1000 nanometers
A nanometer = 1000 picometer

Question 15

What happens to the enzyme if the temperature is too high?

Answer 15

This increases the rate of reaction at first but if it gets to hot, the bond holding the enzymes together break. This changes the shape of the enzyme’s active site so the substrate won’t fit anymore. The enzyme is said to be denatured. All enzymes have an optimum temperaure that they work best at.

Question 16

What is the cell membrane?

Answer 16

It controls the movement of substances in and out of the cell.

Question 17

What is active transport?

Answer 17

Active transport moves particles from low to higher concentration.

Question 18

What do you do with all the results for the osmosis practical?

Answer 18

You need to calulate the percentage change in mass:

Percentage change = (final mass - initial mass / intial mass) x 100

      = (15.1 - 13.2 /13.2) x 100
      = (1.9/13.2) x 100
      = 14.4%

Question 19

What does a permanent vacuole?

Answer 19

Permanent vacuole. Filled with cell sap to help keep the cell swollen.

Question 20

How do you work out total magnification?

Answer 20

Eyepiece lens magnifications x objective lens magnification.

Question 21

What is osmosis?

Answer 21

Osmosis is the diffusion of water across a membrane.

Question 22

Describe the test for starch. (3)

Answer 22

1) Place one spatula of the food sample on a dish or 1 cm3 if the sample is liquid.
2) Using a dropper, place a few drops of iodine solution onto the food.
3) Record any change in the colour of the solution.
It turns blue-black in the presence of starch.

Question 23

Describe the emulsion test for lipids (6)

Answer 23

1) Place two spatulas of the food sample into a test tube or 1 cm3 if the sample is liquid.
2) Add 2 cm3 of ethanol to the tube. Cover the end of the tube and shake the tube vigorously.
3)Allow the contents to settle.
4) Pour the liquid from the top of the mixture into a test tube half-filled with water.
5) Record the level of the food and whether the water is cloudy or clear.
Lipids are detected using the emulsion test. If lipids are present then a milky emulsion will appear.

Question 24

What are light microscopes?

Answer 24

They work by passing light though the specimen. They let us see things like nuclei and chloroplasts and are used to study living cells.

Question 25

How can you investigate the effect of pH on enzyme activity? (8)

Answer 25

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 heat the water until it is 35 ° C (use a thermometer to measure the temperature). Try to keep the temperature constant throughout the experiment.
3) Use a suringe to add 3 cm3 of amylase solution and 1 cm3 of a buffer solution with a pH of 5 to a boiling tube. Using test tube holders, put the boiling tube into the beaker of water and wait for five minutes.
4) Next, use a different syringe to add 3cm3 of a a 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 amylase to break down all the starch. To do this , use a dropping pipette to take a fresh sample from the boiling tube every ten seconds and put a drop into a well. When the iodine solution remains brown-orange, starch is no longer present.
7) Repeat the whole experiment with buffer solutions of different
8) Remember to control any variable each time (for example, concentration and volume of amylase solution) to make it a fair test.

Question 26

List all the sub cellular structures found in both plant and animal cells. (5a+p + 3p)

Answer 26

Cytoplasm
Nucleus
Cell membrane
Mitochondria
Ribosomes
Chloroplast (plant)
Cell wall (plant)
Permanent vacuole (plant)

Question 27

Why is it important for enzymes to break down carbohydrates, proteins and lipids?

Answer 27

Carbohydrates, proteins and lipids are large molecules that are needed by the body for growth, repair and metabolism. They are found in our food. These molecules are too large to pass from the intestine into the blood, so digestive enzymes break them down into smaller molecules. Once in the body, different enzymes use these raw materials to synthesise larger molecules.

Question 28

What is Cell membrane

Answer 28

It is permeable to some substances but not to others and so controls the movement of substances in and out of the cell.

Question 29

List all the sub cellular structures found in bacteria cells. (6)

Answer 29

Chromosomal DNA
Plasmid DNA
Cell wall
Cell membrane
Cytoplasm
Flagellum (not always present)

Question 30

What are Flagella?

Answer 30

Bacteria can have one or more flagella (singular: flagellum). These can rotate or move in a whip-like motion to move the bacterium.

Question 31

How is the sperm cell adapted to its function? (4)

Answer 31

Has a long tail (flagellum) so it can swim to the egg
Lots of mitochondria to provide energy needed to swim to the egg.
Has an acrosome at the ‘head’ to be able to get passed the cell membrane of the egg cell
Has a haploid nucleus

Question 32

How does substrate concentration affect the rate of reaction?

Answer 32

Higher the concentration, the faster the reaction. This is because it is more likely that the enzyme will meet up and react with a substrate molecule. A too high concentration means that all the active sites are full and adding more is making no difference.

Question 33

What is Mitochondria?

Answer 33

Organelles that create chemical energy for the cell to survive.

Question 34

How do you investigate Osmosis using potatoes? (9)

Answer 34

1) Prepare sucrose solutions of different solutions from pure water to a very concentrated sucrose solution.
2) Use a cork borer to cut a potato into same sized pieces (pieces need a diameter of 1cm and preferably from the same potato).
3) Divide the cylinders into groups of three and use a mass balance to measure the mass of each group.
4) Place one group in each solution.
5) Leave the cylinders in the solution for at least 40 minutes (making sure they all get the same mount of time).
6) Remove the cylinder and pat dry gently with a paper towel. This removes excess water from the surface of the cylinder, so you get a more accurate measurement of the final masses.
8) Weigh each group again and record your results.
9) The only thing that you should change in this experiment is the sucrose solution. Everything else (e.g. the volume of solution, the size of the potato cylinders, the type of potatoes used, the amount of drying, etc.) must be kept the same or your results won’t be valid.

Question 35

What does resolution mean in terms of microscopy.

Answer 35

This is where how well a microscope distinguishes between two points that are close together. A higher resolution means that the image can be seen more clearly and in more detail.

Question 36

Describe the Biuret test for proteins (6)

Answer 36

1) Place one-two spatulas of the food sample into a test tube or 1 cm3 if the sample is liquid. Add about 1 cm3 depth of water to the tube and stir to mix.
2) Add an equal volume of potassium hydroxide solution to the tube and stir.
3) Add two drops of copper sulfate solution and stir for two minutes.
4) Record the colour of the solution.
Proteins are detected using Biuret reagent; Sol will be purple if present and blue if not

Question 37

What do calorimeters measure and what are they used for?

Answer 37

Small samples of material are placed in the machine which burns them. The energy given off when the material burns is measured.

Calorimeters are often used in the food industry to measure the energy in food. This value is given in joules or calories in the nutritional information panel on the food packaging.

Question 38

What is Cytoplasm?

Answer 38

It is where many of the chemical reactions happen.

Question 39

What is diffusion?

Answer 39

Particles in a liquid and a gas move continuously. Because of this movement, particles will spread themselves evenly throughout a liquid or a gas.

If there is a situation where particles of a substance are in a higher concentration, they will therefore move from this region to where they are in a lower concentration. This is called diffusion.

Question 40

What is the substrate?

Answer 40

The molecule changed in the reaction

Question 41

How is the ciliated epithelal cell adapted to its function?

Answer 41

These cells have hair-like structures (cilia) which beat to move substances in one direction, along the surface of the tissue.

Question 42

What is the nucleus?

Answer 42

Contains genetic material, including DNA, which controls the cell’s activities.

Question 43

What is chloroplast?

Answer 43

Organelle that contains the green pigment, chlorophyll, which absorbs light energy for photosynthesis. Contains the enzymes needed for photosynthesis.

Question 44

What is a cell wall?

Answer 44

Plant and bacterial cell walls provide structure and protection. Only plant cell walls are made from cellulose.