Topic 1 - Key Concepts In Biology

Question 1

1.1 - How are sub-cellular structures of eukaryotic cells related to their function?

Answer 1

A cell with a nucleus is a eukaryotic cell.
Animal cells are eukaryotic and have a:
Nucleus - controls the cell and its activities, contains DNA.
Cell membrane - Controls what enters and leaves the cell.
Mitochondria - Where aerobic respiration happens.
Cytoplasm - A jelly-like substance where chemical reaction occur.
Ribosomes - Found in the cytoplasm, where they make new proteins.

Another eukaryotic cell is a plant cell, they contain everything an animal cell has but also has:
Cell wall - made of cellulose and maintains rigidity of the cell.
Chloroplasts - contain chlorophyll which traps energy transferred from the Sun for photosynthesis.
Vacuole - contains cell sap to help the rigidity of the cell.

Question 2

1.1 - How are sub-cellular structures of prokaryotic cells related to their function?

Answer 2

A cell without a nucleus, mitochondria and chloroplasts is a prokaryotic cell.
Bacterial cells are prokaryotic and have a:
Chromosomal DNA - controls most cell activities.
Plasmid DNA - controls come cell activities.
Cell membrane - Controls what enters and leaves the cell.
Ribosomes - Found in the cytoplasm, where they make new proteins.
Flagella - Spins for the bacterium to move.

Question 3

1.2 - How are reproductive cells specialised for reproduction?

Answer 3

Sperm cells - lots of mitochondria in the middle of the body, to release energy for the tail.
Head contains a vacuole called the acrosome, which has enzymes that break down the egg cell’s outer layer.
Has streamlined shape and tail moves side to side to swim.

Egg cells - after fusing with a sperm, the membrane becomes hard, to stop more sperm cells entering the egg.
Its cytoplasm is packed with nutrients, to supply the fertilised egg cell for growth of the embryo.

Ciliated epithelial cells - Fertilisation happens in the oviduct of a female.
Cells in oviduct lining transport egg cells to the uterus.
These cells are adapted by having hair-like cilia, which wave from side to side to move substances.
Cells lining the body are epthelial cells, if they have cilia, they are ciliated epithelial cells.

Question 4

1.2 - What happens during reproduction?

Answer 4

Two specialised cell/gametes fuse to create a cell that becomes an embryo.
Human gametes are the egg and sperm cell.
Human nuclei usually contain two copies of 23 chromosomes, these are diploid cells.
Gametes only have one copy of 23 chromosomes, these are haploid cells.

Question 5

1.3 - How has the development of microscopes allowed better research?

Answer 5

The light microscope developed by Hooke had a magnification of 30x.
The resolution is the smallest distance between two points.
Nowadays, there are better lenses and light for microscopes, this makes the light microscope magnify up to 1500x and a resolution of 0.0001mm.
Although the electron microscope uses beams of electrons through a specimen, it can magnify up to 2,000,000 and a resolution of 0.0000002mm or 2 * 10^7.
This microscope allows more detail and clarity.

Question 6

1.4 - How can we find out the magnification of a microscope and estimate cell sizes?

Answer 6

Magnification = Eyepiece * Objective lens
The circular area seen in a microscope is the field of view,
If we know the diameter of the field of view, you can find the length of cells using ratios.
Scale Bars are shown on micrographs to estimate sizes.

Question 7

1.5 - What units are used for small sizes?

Answer 7

milli - 10^-3
micro - 10^-6
nano - 10^-9
pico - 10^-12

divide by 1000 every time.

Question 8

1.6 - Core Practical: Investigate biological specimens using microscopes

Answer 8

Peel the epidermis of an onion cell using tweezers.
Add an iodine stain to the centre of a microscope slide.
Place the specimen on the stain and use a toothpick to lower a coverslip on the specimen. This keeps the specimen flat and in place.
Examine the specimen from lowest to highest magnification.
Draw the cells seen and annotate the structures of it.

Question 9

1.7 - Explain how an enzyme works

Answer 9

Enzymes are 3D proteins formed by amino acids, this 3D shape is caused by the folding of the chain.
This 3D shape is important as in it, there is a pocket called the active site.
The active site is where the substrate of the enzyme fits at the start of a reaction.
Different substrates have different shapes and different enzymes have different active site shapes.
Therefore enzymes only work with specific substrates that fit the active site.

Question 10

1.7 - What is the lock and key model?

Answer 10

A model of how an enzyme and substrate fit together.
The active sire holds the molecules in position for bonds to form and make a product.
Product molecules are slightly different shapes so it no longer fits tightly in the active site and is released.

Question 11

1.8 - How can enzymes be denatured?

Answer 11

Changes in pH or temperature can affect how a protein folds and its shape.
If the shape of the enzyme changes too much, the substrate won’t fit.
If the active site changes shape too much, the enzyme won’t catalyse the reaction.
These changes denature the enzyme.

Question 12

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

Answer 12

pH - Rate of reaction is highest at the optimum pH, at pH’s below and above the optimum, the active site’s shape is affected and the enzyme isn’t as active.

Substrate concentration - At high concentrations, most enzyme active sites have enough of the substrate and the rate of reaction is fast as it can be.
At low concentrations, many enzyme molecules have empty active sites so rate of reaction is slow.

Temperature - As it increases, molecules move faster. Higher speeds increase chance of substrate molecules colliding into enzyme molecules where they react.
When temperature is too high, the shape of the enzyme molecule changes making it harder for a substrate to fit in the active site.
The temperature where the enzyme works the fastest is the active site.

Question 13

1.10 - Core Practical : Investigate the effect of pH on enzyme activity

Answer 13

Set up a heating apparatus with a tripod, gauze, heat resistant mat, Bunsen burner and large beaker half-filled with water.
Heat water to 40°C and keep the temperature constant.
Place a drop of iodine solution into each depression of a well tray.
Measure 2cm^3 of amylase solution into a tube.
Add 1cm^3 of a solution with a noted pH into the tube.
Add 2cm^3 of starch solution to the tube and place in water bath. Start timer and stir.
Add a drop of the solution to the tray every 20 seconds. Stop when iodine changes colour.
Blue/Black colour indicated the presence of starch, so the amylase didn’t work.
Yellow/Orange colour indicates the reaction is complete, so the amylase worked.
Repeat the experiment using different pH’s.

Question 14

1.11 - How do you calculate the rate of enzyme activity on a graph?

Answer 14

If 100g of starch is broken down in five mins, reading off a graph:
100/5 = 20g/min is the rate of reaction.

Question 15

1.12 - How are foods broken down into monomers?

Answer 15

Digestive enzymes turn large molecules into smaller molecules, these smaller molecules are absorbed into the small intestine.
Proteins are broken down into amino acids.
Starch molecules are broken down into glucose molecules.
Lipid molecules are broken into fatty acids and glycerol.

Question 16

1.12 - Why is biological catalysts important in the synthesis and breakdown of foods?

Answer 16

Small molecules build large molecules in tissues, this is synthesis.
The breakdown of large molecules happen slowly and happens only if there is enough energy to break.
Synthesis also happens very slowly, as subunits collide rarely with enough force and right direction to form a bond.
As these reactions are too slow, catalysts speed up breakdown and synthesis.
These catalysts work on substrates and increase rate of reaction.

Question 17

1.12 - Describe some enzymes and the reactions they catalyse

Answer 17

Amylase - Found in saliva and small intestine, breaks down starch into small sugars.
Protease - Found in stomach, pancreas small intestine and breaks down proteins.
Carbohydrase - Found in mouth, pancreas and small intestine and breaks down carbohydrates.
Lipase - Found in pancreas and small intestine and breaks down lipids into fatty acids and glycerol.

Question 18

1.13B - Core Practical : Investigate the use of chemicals to identify starch, reducing sugars, proteins and fats

Answer 18

Iodine solution changes from yellow-orange to blue-black in the presence of a solution with starch
All sugars are reducing sugars, when food is mixed with Benedict’s solution and placed in a water bath, the solution changes colour from blue to red.
In the biuret test, potassium hydroxide and two drops of copper sulfate is added to the solution of food, if the blue solution turns purple, it means protein is present.
Lipids can be tested for using the ethanol emulsion test.
Food is mixed with ethanol and shaken, some of the mixture is poured into water and shaken again.
The fats dissolved in ethanol makes a precipitate or cloudy emulsion over the water, indicating lipids are present.

Question 19

1.14B - Explain how energy in food can be measured

Answer 19

Food contains fats and sugars which are good sources of energy, this can be measured by burning the food in a calorimeter.
The energy transferred from the burning food to the water is calculated by the increase in temperature of the water.

Question 20

1.15 - Explain how substances are transported in and out of cells

Answer 20

Diffusion is the overall movement of particles from a higher concentration to a lower concentration.
It allows small molecules like oxygen to move in and out of cells.
The difference between the two concentrations is the concentration gradient.
Bigger the difference between the concentrations, steeper the concentration gradient and faster the rate of diffusion.

Osmosis is the overall movement of water molecules from a more dilute solute concentration to a more concentrated solution of solute across a semi-permeable membrane.
When both sides of the membrane have equal concentration of solute, the osmosis stops.

Active transport is the movement of particles from a lower concentration to a higher concentration across the concentration gradient, this requires energy.
Active transport happens when cells need to transport molecules against the concentration gradient.

Question 21

1.16 - Core Practical : Investigate osmosis in potatoes

Answer 21

Label separate boiling tubes of sucrose concentration you will test on a rack.
Cut similar sized potatoes, one piece per tube.
Blot each piece dry and record its mass and put each in an empty tube.
Add the sucrose solutions, make sure the potatoes are covered.
After 15 mins, remove each piece and blot it dry, record their masses again.

Question 22

1.17 - How do you calculate percentage changes of mass in osmosis?

Answer 22

work out the difference between final and starting mass.
divide by initial mass.
times by 100.