SB1 - Key Concepts in Biology ✓

Question 1

SB1b CP - How do you use use a microscope?

Answer 1

• 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 2

SB1a - What determines how good a microscope is at showing small details?

Answer 2

• Magnification: How much it can zoom in

- Resolution: The smallest distance between two distinctly different points

Question 3

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

Answer 3

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

Question 4

SB1a - SI units - For Chris’s benefit

Answer 4

• milli = x10^-3
• micro= x10^-6
• nano=x10^-9
• pico=x10^-12

Question 5

SB1b - How are animal cells different to plant cells?

Answer 5

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 6

SB1b - What do the sub-cellular structures in eukaryotic cells do?

Answer 6

• 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
• Vacoule: Stores cell sap

Question 7

SB1c - What are the adaptations of the following cells:

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

Answer 7

• 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 absroption easier

Question 8

SB1c - What is the function of a gamete?

Answer 8

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

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

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

Answer 10

Eukaryotic cells have a nucleus, prokaryotic cells do not

Question 11

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

Answer 11

Enzymes are biological catalysts that speed up reactions. They break down protiens/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 12

SB1g - How do enzymes work?

Answer 12

Each type of enzyme is in a shape that is specific to their substrate. Once they connect to their substrate, it’s shape changes and they can no longer bond. THe idea that an enzyme bonds with a specific substrate is the lock-and-key mechanism

Question 13

SB1e - What is a polymer?

Answer 13

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 14

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

Answer 14

• 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 15

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

Answer 15

• Starch: Iodine will go from yellow to blue-black
• Proteins: Biruet’s solution will go from blue to purple
• Lipids- Add ethanol and shake and a white emulsion-fatty layer - should form is 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 16

SB1f- How can we use a calorimeter?

Answer 16

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 17

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

Answer 17

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 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 - How is enzyme activity affected by temperature, pH and substrate concentration?

Answer 19

Temperature: As temperature increases, molecules move faster and so more successful collisions occur between enzymes and substrates so the rate of reaction increases. Until the temperature causes the enzyme to change shape causing it to denature

pH: An enzyme has an optimum pH where it works best. The furhter away from this, it will get slower till it becomes denatured

Substrate concentration: Increasing this will increase the rate of reaction as there are more collisions occurring. This is until a point when all enzymes are full up and rate of reaction will no longer increase

Question 20

SB1i - What is the difference between diffusion and osmosis?

Answer 20

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 21

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

Answer 21

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 22

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

Answer 22

• 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 agreates difference between water concentration as osmosis works with the concentration gradient

This can work with any semi-permeable membrane