SB1 - Key Concepts in Biology ✓

Question 1

SB1a - How do you calculate Actual Size?

Answer 1

Image Size / Magnification

Question 2

SB1a - How do you calculate total magnification in a light microscope?

Answer 2

Objective Lens x Eyepiece Lens

Question 3

SB1a - List 3 differences between Light and Electron Microscopes

Answer 3

Electron microscopes produce a much higher resolution image due to the shorter wavelength of electrons
Light Microscopes can show a true colour whereas electron microscopes will show a black and white image since electrons don’t have a colour spectrum
Light microscopes can use a live specimen whereas electron microscopes have to use dead specimens due to electrons having to pass through a vacuum

Question 4

SB1a - What 2 things determine how good a microscope is at showing small details?

Answer 4

Magnification: How much it can zoom in
Resolution: The smallest distance between two distinctly different points

Question 5

SB1a - What has the development of the electron microscope allowed us to do?

Answer 5

It has allowed us to see sub-cellular structures as they have a much more powerful resolution and magnification

Question 6

SB1b - How are animal cells different to plant cells?

Answer 6

Animal cells, do not have cell walls, chloroplasts or vacuoles like plants do.
They only have nuclei, ribosomes, mitochondria, cytoplasm and a cell surface membrane.

Question 7

SB1b - Describe the function of each of these subcellular organisms in Eukaryotic cell:

Cell Membrane -

Nucleus -

Cytoplasm -

Mitochondria -

Ribosomes -

Cell Wall -

Chloroplasts-

Vacuole -

Answer 7

Cell membrane: controls what enters and leaves the cell
Nucleus: contains DNA that controls cell activities
Cytoplasm: fills the cell and where reactions occur
Mitochondria: Where respiration takes place
Ribosomes: Where protein synthesis takes place Plant only:
Cell wall: Protects the cell
Chlorplasts: Contain chlorophyll used in photosynthesis
Vacuole: Stores cell sap

Question 8

SB1b CP - How do you use use a microscope?

Answer 8

Put a thin sample of tissue (e.g. onion epidermis) onto a microscope slide
Add a few drops of a suitable stain/dye (e.g. iodine), so that the sample can be seen
Place a coverslip on top of the tissue and place the slide onto the microscope stage.
Use the objective lens with the lowest magnification, and focus on the sample.
Increase the magnification and refocus to see different features of the cell.
If you record the image you see, note down the magnification it was taken at

Question 9

SB1c - What are the adaptations of the following cells:

Egg cell
Sperm cell
Cilliated epithelial cell
Cells lining the small intestine

Answer 9

Egg cell: Has a haploid nucleus, with a special cell membrane to allow only one sperm cell in and many nutrients in its cytoplasm
Sperm cell: Has an acrosome with enzymes to penetrate the egg cell with lots of mitochondria and a tail to swim
Ciliated epithelial cell: Lined with cilia and packed with mitochondria this allows the cell to have a ‘wavy’ movement to move an egg along
Microvilli: The cells lining the small intestine have small folds called microvilli which increase its surface area making absorption easier

Question 9

SB1d - What are the differences between eukaryotic and prokaryotic cells?

Answer 9

A prokaryotic cell will not contain a nucleus, mitochondria or chloroplasts
Eukaryotic cells can be up to x1000 times larger than a Prokaryotic Cell

Question 9

SB1c - What is the function of a gamete?

Answer 9

Gametes are sex cells used in reproduction.
Examples are sperm and egg cell

Question 9

SB1d - What are the functions of structures in bacteria?

Answer 9

Single loop of DNA: Contains chromosomes and genes
Plasmids: Contain additional genes
Flagellum: Used to propel the bacteria
Flexible cell wall: for support
Cytoplasm: Containing prokaryotic ribosomes

Question 10

SB1e - What are enzymes and what are they made up of made up of?

Answer 10

Enzymes are biological catalysts that speed up reactions.
They break down proteins/substances called substrates.
Enzymes are made up of amino acids and they are proteins.
They are needed to speed up reactions we cannot live without

Question 11

SB1e - What are the three main nutrient based enzymes? Where are they found and what do they do?

Answer 11

Amylase: Found in saliva. breaks down starch into Sugar
Protease: Found in the stomach, breaks down proteins into amino acids
Lipase: Found in the stomach and pancreas, breaks down lipids into fatty acids and glycerol

Question 12

SB1e - What is a polymer?

Answer 12

A polymer is a chain of single substances called monomers.
The formation of a polymer is called synthesis.
Enzymes often break down polymers into monomers

Question 13

SB1f CP - What tests are used to identify main components in food?

Starch
Proteins
Lipids
Sugars

Answer 13

Starch: Iodine will go from yellow to blue-black
Proteins: Biruet’s solution will go from blue to purple
Lipids: Add ethanol and shake - a white emulsion-fatty layer should form if it is present
Sugars: Benedict’s solution while heating which will turn anywhere from green to yellow to red, indicating how much sugar is present This is a semi-quantitative test. It mostly gives non-measurable values

Question 14

SB1f- How can we use a calorimeter?

Answer 14

Burn a known mass of the food under a boiling tube filled with a known volume of water.
Calculate the change in temperature of the water.

Question 15

SB1g - How do enzymes work?

Answer 15

Each type of enzyme is in a shape that is specific to their substrate.

They can be re-used as long as they don’t become denatured

The idea that an enzyme bonds with a specific substrate is the lock-and-key mechanism

Question 16

SB1g - What is the function of the active site of an enzyme?

Answer 16

The active site is unique to an enzyme so each enzyme can only work on specific substrates and is where the substrate must be for anything to take place

Question 17

SB1g - What is the lock and key model?

Answer 17

The lock and key model is a model of how enzymes work - it compares enzyme action to a lock and key because of how the substrate and active site fit together

When the substrate binds to the active site, it forms the Enzyme-Substrate complex.

After the enzyme catalyses the reaction, the products are released because they no longer fits tightly into the active site
The enzyme is free to be used again

Question 18

SB1g- How are enzymes denatured?

Answer 18

Changes in pH and temperature can affect the shape of an enzymes active site.

When the active site can no longer accept any substrates, it is said to have become denatured.

Question 19

SB1h - Explain how the rate of enzyme reaction is affected by temperature

Answer 19

At very low temperatures, the particles do not have enough energy to move, so the enzyme is inactive; the rate of reaction is very low
As the temperature increases, particles begin to move more as they gain kinetic energy; the rate of reaction will increase

Eventually, the enzyme reaches an optimum temperature where it is working at it’s fastest
However, if the temperature increases too far beyond that, the active site will begin to change shape and the rate of reaction will decrease

Eventually, if high enough temperatures are reached, the shape of the active site is changed to a point where the substrate is no longer able to bind to it. It becomes denatured.

Question 20

SB1h - How is enzyme activity affected by pH?

Answer 20

An enzyme has an optimum pH where it works best.

The further away from this, it will get slower till it becomes denatured

Question 21

SB1h- Explain how the rate of enzyme action is affected by substrate concentration

Answer 21

At first, the more substance you use, the higher the rate of reaction as it causes more collisions to occur
However, at high concentrations most enzyme active sites contain substrate molecules therefore there is no benefit to adding more substrate, the rate of reaction won’t increase beyond that point

Question 22

SB1i - How do cells transport substances against a concentration gradient?

Answer 22

Using active transport which is carried out by transporter proteins on membranes which require energy to run.
They take in the molecule and then change shape to move it through the membrane.
This works against the concentration gradient

Question 23

SB1i - What is the difference between diffusion and osmosis?

Answer 23

Diffusion is when particles move from a high concentration to a low concentration.
In osmosis this is the same principal except across a semi permeable membrane where a solvent moves from and area of high concentration to an area of low concentration

Question 24

SB1i CP - Describe the method you would use to investigate osmosis through potatoes

Answer 24

Cut discs of raw potato, blot them dry, and measure their mass.
Put each disc in a sugar (or salt) solution of different concentrations
After 30 minutes, measure the mass of each disc again.
Subtract the initial mass from the final mass of each disc.
Divide this number by the initial mass and then multiply by 100 to give a percentage change in mass.
The highest change in mass means there was the greatest difference between water concentration as osmosis works with the concentration gradient This can work with any semi-permeable membrane

Question 25

SB1i CP - Explain why potatoes will gain mass when put into a very dilute solution

Answer 25

The concentration of water in the solution will be higher than the concentration of water in the potatoes, so water will move into the potato by osmosis which increases mass

Question 26

SB1i CP - Explain why potatoes will lose mass when put into a very concentrated solution

Answer 26

The water concentration of the potatoes will be higher than that of the solution, so water will move into the solution due to osmosis. Therefore, the potatoes will lose mass.

Question 27

SB1i - What are the 3 factors affecting Diffusion?

Answer 27

Temperature
Concentration Gradient
Surface Area of Cell Surface Membrane

Question 28

SB1h CP - How do you calculate rate of reaction in enzyme-controlled reactions?

Answer 28

1/time