SB1 - Key Concepts in Biology

Question 1

What is magnification?

Answer 1

The magnification of an image is the number of times larger it appears than it’s actual size (e.g. something viewed under x30 magnification looks 30 times larger than it is in real life). Magnification = magnification of eyepiece lens x magnification of objective lens.

Actual size = image size / magnification

Question 2

What is resolution?

Answer 2

Resolution is the smallest distance between two points that can still be seen as two points.

Question 3

What are the main structures found in animal cells and what do they do?

Answer 3

Animal cells contain a cell membrane, a nucleus, cytoplasm, ribosomes and mitochondria.
Cell membrane - provides structure, selectively permeable (can control what gets in and out of the cell)
Nucleus - contains the cell’s DNA and controls the cell
Cytoplasm - a jelly-like substance in which most of the cell’s chemical reactions take place
Ribosomes - responsible for synthesising protein
Mitochondria - provides energy for the cell through aerobic respiration

Question 4

What are the main structures in plant cells and what do they do?

Answer 4

Plant cells contain a cell wall, a cell membrane, a nucleus, a vacuole, cytoplasm, mitochondria, ribosomes and chloroplasts.
Cell wall - made of cellulose, supports and protects the cell
Cell membrane - selectively permeable (controls what gets in and out of the cell)
Nucleus - contains the cell’s DNA, controls the cell
Cytoplasm - where most of the cell’s chemical reactions occur
Vacuole - stores cell sap and helps the cell to stay firm and rigid
Mitochondria - provide energy for the cell by aerobic respiration
Ribosomes - responsible for protein synthesis
Chloroplasts - contain chlorophyll, which is needed for photosynthesis

Question 5

What are the main differences between plant and animal cells?

Answer 5

Plant cells have chloroplasts, a vacuole and a cell wall, whereas animal cells do not.

Question 6

What are specialised cells?

Answer 6

Specialised cells are cells which have differentiated to fit a particular purpose.

Question 7

How are small intestinal cells specialised?

Answer 7

They have membranes with tiny folds (microvilli), which increase the surface area of the cell, and so speed up digestion.

Question 8

How are cells in the pancreas specialised?

Answer 8

The pancreas produces many enzymes, which are a type of protein. Cells in the pancreas are therefore specialised to have many ribosomes.

Question 9

How are human egg cells specialised for reproduction?

Answer 9

They have a haploid nucleus (contains half of the genetic material) so that when fertilised, the zygote has the full amount of chromosomes, very large to increase chances of fertilisation, jelly coat protects the egg cell and hardens after fertilisation to ensure that only one sperm cell enters the egg cell, cytoplasm is packed with nutrients to supply the fertilised egg with the energy and materials needed for growth and development of the embryo.

Question 10

How are human sperm cells specialised for reproduction?

Answer 10

They have a haploid nucleus so that the embryo has the correct number of chromosomes, streamlined shape, tip of head has an acrosome which contains enzymes which break down the jelly coat of the egg cell, lots of mitochondria to produce lots of energy needed for the cell to travel long distances relative to its size, flagellum moves from side to side, allowing the sperm cell to swim.

Question 11

How are cells in the oviduct and trachea specialised to their functions?

Answer 11

Ciliated epithelial cells are found in the oviduct and the trachea. They have hair-like structures called cilia on their surfaces, which wafts substances (in the trachea, the substance is mucus, in the oviduct, the substance is egg cells).

Question 12

What are the structures in bacterial cells and what do they do?

Answer 12

Bacteria contain a cell wall, a cell membrane, cytoplasm, chromosomal DNA, plasmids (bacteria are prokaryotes so don’t have a nucleus), some have a slime coat, some have flagellum.
Cell wall - for support, made of peptidoglycan
Slime coat - for protection
Chromosomal DNA - contains most of the cell’s genetic material
Plasmids - contain the rest of the cell’s DNA

Question 13

What are enzymes?

Answer 13

Enzymes are biological catalysts (they speed up reactions by lowering the activation energy) and can be used to break down or combine reactants into different products.

Question 14

What does protease do?

Answer 14

Protease beaks down proteins into amino acids.

Question 15

What does amylase do?

Answer 15

Amylase breaks down starch into sugars

Question 16

What does lipase do?

Answer 16

Lipase breaks down lipids onto glycerol and fatty acids.

Question 17

How do you test for reducing sugars?

Answer 17

Mix an equal volume of food solution with Benedict’s solution and place in a hot water bath for a few minutes. If it is blue, there is no reducing sugars, green means very little reducing sugars, orange means more reducing sugars, red means lots of reducing sugars.

Question 18

How do you test for protein?

Answer 18

Biuret test - potassium hydroxide is mixed with a solution of food, two drops of copper sulphate solution are added. If the pale blue solution turns purple, there is protein in the food.

Question 19

How do you test for lipids?

Answer 19

Ethanol emulsion test - the food is mixed with ethanol and shaken, this is poured into water and shaken again. If it goes cloudy, there are lipids in the food.

Question 20

How do you test for starch?

Answer 20

Iodine solution changes colour from yellow-orange to blue-black when in contact with starch.

Question 21

How do you test the calorie content of food?

Answer 21

Burn a known volume of food over a known volume of water. Record the temperature of the water before you start and after all the food has burned. The temperature change is used to calculate the calorie content of the food.

Question 22

How do enzymes work?

Answer 22

The active site of the enzyme is complementary to the substrate, meaning that the substrate can fit into the enzyme’s active site, where it is broken down or formed. A large change in pH or temperature can affect the shape of the active site. If the shape changes too much, the substrate will no longer fit and the enzyme will not work anymore. It is said to be denatured.

Question 23

How can the rate of a reaction be calculated?

Answer 23

Rate = amount of reactant used OR amount of product formed / time

Question 24

Which factors affect the rate of enzyme activity?

Answer 24

Temperature - the higher the temperature, the more kinetic energy the enzymes have, the faster they move, so more collisions between enzyme and substrate occur. However, too high a temperature will cause the enzyme to be denatured
pH - the closer the pH value is to the enzyme’s optimum pH, the faster the reaction will go, too high or low a pH will cause the enzyme to denature.
Concentration of substrate - initially, a higher concentration of substrate will increase the rate of reaction, as more enzyme-substrate collisions will occur, however eventually the rate will plateau as all the active sites will be in use so the reaction cannot go any faster.
Concentration of enzymes - initially, a higher concentration of enzymes will increase the rate as more enzyme-substrate collisions occur, however eventually the rate will plateau as all of the substrate is being broken down, so adding more enzymes makes no difference.

Question 25

What is diffusion?

Answer 25

Diffusion is the random movement of particles from an area of high concentration to an area of low concentration.

Question 26

What factors affect the rate of diffusion?

Answer 26

Concentration gradient - the difference between the two concentrations is the concentration gradient, the steeper the gradient is, the faster the rate of diffusion.
Temperature - higher temperatures mean particles have more kinetic energy, so the move faster, meaning the rate of diffusion is also faster.
Surface area - the larger the surface area, the faster the rate of diffusion.

Question 27

What is osmosis?

Answer 27

Osmosis is the net movement of particles from an area of high water concentration to an area of low water concentration (i.e. from a dilute to a concentrated solution) down a concentration gradient and across a semi-permeable membrane.

Question 28

What is active transport?

Answer 28

Active transport is the movement of particles against a concentration gradient, from an area of low concentration to an area of high concentration. This therefore requires energy.

Question 29

Core practical - using microscopes

Answer 29

• collect a small specimen of cells (e.g. tissue from onions, cheek cells)
• add a few drops of a suitable stain to a slide
• place the specimen on top of the stain and add a coverslip
• examine the specimen by first focusing using the lowest magnification then working your way up
• draw the cells you see and annotate

Question 30

Core practical - testing foods

Answer 30

• prepare a solution of each food in water
• carry out the appropriate food test
• record the results

Question 31

Core practical - pH and enzymes

Answer 31

• set up heating apparatus using a tripod, heat mat, gauze, Bunsen burner and large beaker half-filled with water.
• heat the water to 40 degrees then turn Bunsen burner to safety flame (to maintain the temperature)
• place one drop of iodine solution into each depression of a dimple tile
• measure 2cm3 of amylase solution into a tube
• add 1cm3 of a solution with a known pH into the tube.
• add 2cm3 starch solution to the tube and place it in the water bath. Start the stop clock
• every 20 seconds, take a small amount of the mixture and put it in a fresh drop of iodine solution. Stop testing when the iodine stops changing colour.
• repeat the experiment multiple times with different pHs, the less time taken for the iodine solution to stop changing colour, the closer the pH was to amylase’s optimum pH.

Question 32

Core practical - osmosis in potato slices

Answer 32

• label separate boiling tubes with the sucrose concentration of each solution to be tested, put them in a rack.
• cut similar sized slices of potato enough for one per tube (make sure they will fit)
• blot each potato piece dry and record their masses, then put one in each empty tube
• fill each tube with the solutions of labelled concentrations (ensure each potato piece is fully covered)
• after at least 15 minutes, remove each potato piece and blot it dry, record the mass again