Key Biology Concepts

Question 1

What is the function of the nucleus?

Answer 1

To contain the cell’s DNA and to control the cell’s functions

Question 2

What is the function of the ribosome?

Answer 2

To synthesise proteins from amino acids using mRNA

Question 3

What is the function of the cell membrane?

Answer 3

To control what substances go in and out of the cell

Question 4

What is the function of the cell wall?

Answer 4

Made of cellulose, it protects the cell and gives it shape

Question 5

What is the function of the chloroplasts?

Answer 5

To contain chlorophyll, a chemical to allow photosynthesis in the chloroplasts

Question 6

What is the function of the large vacuole?

Answer 6

It contains a cell sap, a weak solution of sugar and salts. It maintains the internal pressure to support the cell.

Question 7

What is the function of the mitochondria?

Answer 7

To perform respiration for the cell, which produces energy

Question 8

What are the differences between prokaryotic and eukaryotic cells?

Answer 8

Eukaryotic cells are complex and include all plant and animal cells. They have a nucleus and are usually multicellular, making up a eukaryote
Prokaryotic cells have no nucleus but rather chromosomal DNA and are smaller and simpler e.g. bacteria. A prokaryote is a prokaryotic cell as it is unicellular

Question 9

What are acrosomes and how do they help the sperm cell to function?

Answer 9

An acrosome is an organelle that forms over the head of the sperm cell. It contains digestive enzymes that break down the outer membrane of the ovum so that the sperm cell’s nucleus can fuse with that of the egg cell (fertilisation).

Question 10

How does an egg cell membrane change after fertilisation?

Answer 10

Once one sperm cell has fertilised the egg cell, the egg cell’s plasma membrane rapidly depolarises, preventing other sperm from fusing with the egg cell and fertilising it

Question 11

How is a ciliated epithelial cell adapted to its function?

Answer 11

It lines the surfaces of organs
Some have cilia on it which wag from side to side, which pulls away dust, mucus and bacteria.
It is flat so that cilia cells can interlock and cover surfaces completely.

Question 12

How has the microscope developed over time?

Answer 12

Light microscopes were invented in the 1590s and pass light through the specimen, allowing us to see large parts of the cell e.g. the nucleus and chloroplasts.
Electron microscopes were invented in the 1930s and use electrons. They have a much higher resolution and magnification, allowing us to see more subcellular structures in greater detail

Question 13

How is magnification calculated?

Answer 13

Magnification = Image size/ real size

Question 14

What are millimetres, micrometres, nanometres and picometers in standard form and how do you convert from one to another?

Answer 14

Millimetres - x10-3m
Micrometres - x10-6m
Nanometres - x10-9m
Picometres - x10-12m

To go one bigger divide by 1000 and to go one smaller multiply by 1000

Question 15

What is the lock and key hypothesis?

Answer 15

The hypothesis that one substrate can only fit into one enzyme, similar to how one key can only fit into one lock

Question 16

What are enzymes?

Answer 16

Biological catalysts that speed up the rate of or lower the activation energy of reactions, reducing the need for high temperatures

Question 17

What is the active site?

Answer 17

The place where enzymes and substrates meet

Question 18

Why does temperature, pH and substrate concentration affect the rate of an enzyme reaction.

Answer 18

At certain amounts of the three, the enzyme will work most efficiently, but at extreme concentrations of the three, the enzyme will change its shape so it will no longer work: it is denatured.

Question 19

What enzymes break down starch, proteins and lipids? What do they get broken into?

Answer 19

Starch: amylase -> maltose and other sugars
Proteins: protease -> amino acids
Lipids: lipase -> glycerol and fatty acids

Question 20

What chemical reagents are used to test for proteins, reducing sugars, starch and fats?

Answer 20

Proteins: Biuret’s solution
Reducing sugars: Benedict’s solution
Starch: Iodine
Fats: Water and ethanol

Question 21

How is a calorimeter used to measure the energy in foods?

Answer 21

Food is set alight and oxygen is provided to keep the fire going
The food is put under a boiling tube of water, which heats up water in it
After the fire goes out the change in water temperature is measured
This shows you how much energy is in foods

Question 22

What factors affect the rate of diffusion?

Answer 22

The concentration gradient
Temperature
The distance particles must travel
Particle size

Question 23

What is diffusion?

Answer 23

The net movement of particles from an area of high concentration to an area of low concentration until even distribution is reached

Question 24

What are the differences between diffusion and active transport?

Answer 24

Diffusion happens from an area of high concentration to an area of low concentration down the concentration gradient. It is a passive process and does not require energy. Active transport happens from an area of low concentration to an area of high concentration. It is an active process and requires energy.

Question 25

What is the function of the cytoplasm?

Answer 25

A gel like substance where most chemical reactions happen

Question 26

What is the function of chloroplasts?

Answer 26

They contain chlorophyll and are where photosynthesis happens, which makes food for the plant

Question 27

What are the parts of animal and plant cells?

Answer 27

Animal cells: nucleus, cytoplasm, cell membrane, mitochondria, ribosomes
Plant cells: all of the above plus cell wall, a large vacuole, chloroplasts

Question 28

What are the parts of a bacterial cell?

Answer 28

Chromosomal DNA (one long circular chromosome)
Ribosomes
Cell membrane
Plasmid DNA (small loops of extra DNA, which give functions such as drug resistance)
Flagellum (a hair like structure that rotates to move the bacterium)

Question 29

What are the adaptations of a sperm cell?

Answer 29

Long tail to swim
Lots of mitochondria in the middle section to provide energy
An acrosome
A haploid nucleus

Question 30

What are the adaptations of the egg cell?

Answer 30

Nutrients in the cytoplasm to feed the embryo
A haploid nucleus
A membrane that changes structure after fertilisation to stop any more sperm getting in

Question 31

How do you calculate total magnification?

Answer 31

Total magnification = eyepiece lens magnification x objective lens magnification

Question 32

How do you view a specimen using a light microscope?

Answer 32

Take a thin slice of the specimen. Put a drop of water on a clean slide to secure in and put the specimen in place with tweezers. Add a stain to the specimen if it is transparent. Put a cover slip on. Clip the slide onto the stage. Select the lowest power objective lens and move the stage up. Move the stage down until it is in focus.

Question 33

How do you create a scientific drawing of a specimen?

Answer 33

Use a sharp pencil
Draw outlines of the main features
Use clear, unbroken lines
Do not shade
Take up most of the space
Label with straight lines that do not cross
Include the magnification and scale

Question 34

What is a substrate?

Answer 34

The molecule changed in the reaction using an enzyme

Question 35

How does temperature affect the rate of reaction with enzymes?

Answer 35

At low temperatures the substances little energy so reactions are slow. As temperature increases, the reaction rate speeds up. However, after a point some of the bonds holding enzymes together break down, changing the shape of the active sight. The enzyme is denatured so no reactions can happen.

Question 36

How does pH affect the rate of reaction with enzymes?

Answer 36

If the pH is too high or too low it interferes with the bonds holding the enzyme together, changing the shape of the active site and denaturing it. All enzymes have an optimum pH.

Question 37

How does substrate concentration affect the rate of reaction with enzymes?

Answer 37

At low concentrations the enzyme is not likely to meet and react with substrate molecules, so reaction rate increases to a point, where all the active sites are full.

Question 38

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

Answer 38

Put a drop of iodine solution into every well of a spotting tile. Use a Bunsen burner to heat water in a beaker to 35 degrees. Add amylase solution and buffer solution with pH5 to a boiling tube and place it in the beaker. Wait, then add starch solution. Start a stopwatch and take a sample every 10 seconds and add it to a drop in the well. If starch is present it will change from brown/orange to blue/black; if it does not, the starch has broken down. Repeat with different pHs.

Question 39

How do you calculate rate of reaction?

Answer 39

Rate = 1000 / time

Question 40

What is the Benedict’s test?

Answer 40

Add Benedict’s reagent (blue) to a sample and heat it in a water bath to 75 degrees. It will form a coloured precipitate if reducing sugars are present.
As concentration increases the colour turns from:
Blue to green to yellow to orange to brick red

Question 41

What is the test for starch?

Answer 41

Add iodine solution to the sample. If starch is present, it will change from brown/orange to blue/black

Question 42

What is the test for lipids?

Answer 42

Shake the substance with ethanol for about a minute until it dissolves, then pour the solution into water. Lipids will precipitate out of the liquid and form a milky emulsion; the more lipid, the more noticeable the milky colour.

Question 43

What is the test for proteins?

Answer 43

Biuret test:
Add a few drops of potassium hydroxide to make the solution alkaline. Add copper(II) sulphate (bright blue). Protein will turn the solution purple.

Question 44

What is the equation for calculating energy in food?

Answer 44

Energy in food (J) = Mass of water (g) x temperature change (degrees C) x 4.2

Question 45

What is osmosis?

Answer 45

The net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration

Question 46

What is active transport?

Answer 46

The movement of particles across a membrane against a concentration gradient using energy

Question 47

How can you investigate osmosis in potatoes?

Answer 47

Prepare sucrose solutions of different concentrations ranging from pure water to very concentrated. Cut a potato into same sized pieces. Divide the cylinders into groups of three and measure the mass of each group. Place one group in each solution and wait. Remove the cylinders and pat dry with a paper towel. Weigh each group again and calculate the change in mass.