Topic 1 – Key Concepts in Biology

Question 1

What is the function of the nucleus?

Answer 1

-Contains DNA coding for a particular protein needed to build new cells.

Question 2

What is the function of the cytoplasm?

Answer 2

• Liquid substance in which chemical reactions in the cell occur.
  -Contains enzymes and organelles are found in it

Question 3

What is the function of the cell membrane?

Answer 3

-Controls what enters and leaves the cell

Question 4

What is the function of the mitochondria?

Answer 4

-Where aerobic respiration reactions take place, providing energy for the cell.

Question 5

What is the function of the ribosomes?

Answer 5

-Where Protein synthesisoccurs

Question 6

What is the function of the chloroplasts?

Answer 6

-Where photosynthesis takes place , providing food for the plant.
-contains chlorophyll pigment, which harvest the light for photosynthesis.

Question 7

What is the function of the vacuole?

Answer 7

-contains cell sap
-improves cell’s rigidity

Question 8

What is the function of the cell wall?

Answer 8

-made from cellulose
-provides strength to the cell

Question 9

What is the function of the chromosomal DNA?

Answer 9

-This floats in the cytoplasm, as bacterial cells have no nucleus

Question 10

What is the function of the flagella?

Answer 10

-Long thin ‘whip-like’ tails, that allow bacterial cells to move

Question 11

How do cells specialise?

Answer 11

Cells specialise by undergoing differentiation: a process that involves the cell gaining new sub-cellular structures in order for it to be suited to its role. In animals, most cells differentiate once, but in plants many cells retain the ability.

Question 12

How are sperm cells specialised?

Answer 12

Sperm cells: specialised to carry the male’s DNA to the egg cell (ovum) for successful reproduction

-Streamlined head and long tail to aid swimming

-Many mitochondria (where respiration happens) which supply the energy to allow the cell to move

-The acrosome has digestive enzymes which break down the outer lavers of membrane of the egg cell

-Haploid nucleus - the word haploid simply means that it has 23 chromosomes, rather than the 46 that most other body cells have

Question 13

How are egg cells specialised?

Answer 13

Egg cells: specialised to accept a single sperm cell and develop into an embryo

-Surrounded by a special cell membrane which can only accept one sperm cell (during fertilisation) and becomes impermeable following this

-Lots of mitochondria to provide an energy source for the developing embryo

-Large size and cytoplasm to allow quick, repeated division as the embryo grows

Question 14

How are Ciliated epithelial cells specialised?

Answer 14

Ciliated epithelial cells: specialised to waft bacteria (trapped by mucus) to the stomach

Long, hair-like processes called cilia waft bacteria trapped by sticky mucus (produced by nearby goblet cells) down to the stomach, where they are killed by the stomach acid. This is one of the ways our body protects against illness.

Question 15

How are root hair cells specialised?

Answer 15

Root hair cells: specialised to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots.

-Have a large surface area due to root hairs, meaning more water can move in

-The large permanent vacuole affects the speed of movement of water from the soil to the cell

-Mitochondria to provide energy from respiration for the active transport of mineral ions into the root hair cell

Question 16

How are Xylem cells specialised?

Answer 16

Xylem cells: specialised to transport water and mineral ions up the plant from the roots to the shoots

-Upon formation, a chemical called lignin is deposited which causes the cells to die. They become hollow and are joined end-to-end to form a continuous tube so water and mineral ions can move through

-Lignin is deposited in spirals which helps the cells withstand the pressure

Question 17

How are phloem cells specilaised?

Answer 17

Phloem cells: specialised to carry the products of photosynthesis (food) to all parts of the plants

-Cell walls of each cell form structures called sieve plates when they break down, allowing the movement of substances from cell to cell

-Despite losing many sub-cellular structures, the energy these cells need to be alive is supplied by the mitochondria of the companion cell

Question 18

What are the three common calculations in microscopy?

Answer 18

1. magnification of a light microscope: Magnification of an eye piece lens x magnification of objective lens
   2.size of an object: size of image/magnification = size of object
   3.magnification = measured size/actual size

Question 19

what are the prefixes of measurement?

Answer 19

Prefix: Multiply unit by:
centi 10^-2
milli 10^-3
micro 10^-6
nano 10^-9
pico 10^-12

Question 20

What are the parts of the microscope called?

Answer 20

-Eyepiece - This is the part of microscope that we look through to view specimens.
-Barrel -The upper part of the microscope that can be moved up or down to focus the image. –Turret- The part of the microscope that is rotated to change the magnification lens in use.
-Lens-The lens increases the magnification of the specimen. –Stage -The flat surface on which we place the specimen

Question 21

What are the steps of using a light microscope?

Answer 21

To use a light microscope, you should:

1. Place the slide on the stage and look through the eyepiece lens
2. Turn the focus wheel to obtain a clear image
3. Start with the lowest objective lens magnification
4. Increase the magnification of the objective lens and refocus.

Question 22

How do you prepare a slide?

Answer 22

1. Take a thin layer of cells from your sample by either peeling them off or using a cotton bud
2. Add a small amount of the correct chemical stain (you will be told by your teacher which stain to use). Chemical stains are used to make some parts of the specimen more visible when you look at them through the microscope.
3. Apply the cells to your glass slide by placing them on or wiping the cotton bud against it
4. Carefully lower a coverslip onto your slide, taking care to avoid air bubbles

Question 23

What are enzymes?

Answer 23

Enzymes are biological catalysts, (substances that increases the rate of reaction without being used up)

Enzymes are present in many reactions - allowing them to be controlled. They can both break up large molecules and join small ones

They are protein molecules and the shape of the enzyme is vital to its function.

This is because each enzyme has its own uniquely shaped active site where the substrate binds.

Question 24

What is an enzymes’ optimum temperature, and what is its effect.

Answer 24

The optimum temperature, for enzymes, in humans is a range around 37 degrees Celsius (body temperature).

The rate of reaction increases with an increase in temperature up to this optimum, but above this temperature it rapidly decreases and eventually the reaction stops.

When the temperature becomes too hot, the bonds that hold the enzyme together will begin to break.
This changes the shape of the active site, so the substrate can no longer bind to the enzyme.

Question 25

What is the enzymes’ optimum pH, and what is its effect?

Answer 25

The optimum pH for most enzymes is 7 (neutral), but some, like pepsin, that are produced in acidic conditions, such as the stomach, have a lower optimum pH. If the pH is too high or too low, the forces that hold the amino acid chains that make up the protein will be affected.

The enzyme becomes denatured and the shape of the active site has changed, so the enzyme-substrate complex cannot be formed.

Question 26

What is the Lock and Key Theory?

Answer 26

The Lock and Key Hypothesis (a simplified explanation of how enzymes work):

1. The shape of the substrate is complementary to the shape of the active site (matches the shape of the active site), so when they bond it forms an enzyme-substrate complex.
2. Once bound, the reaction the reaction takes place and the products are released from the surface of the enzyme.

Enzymes can only catalyse (speed up) reactions when they bind to a substrate that has a complementary shape, as this is the only way that the substrate will fit into the active site. This is called enzyme specificity.

Enzymes require an optimum pH and temperature, because they are proteins. They also need an optimum substrate concentration

Question 27

What are the steps to the practical to see the effect of pH on enzyme activity?

Answer 27

1. Place single drops of iodine solution on each well of a tray.
2. Label a test tube with the pH to be tested. Place it in a water beaker with 50ml cold water and place this above a Bunsen Burner for 3 minutes.
3. Place 2cm² of amylase solution, 2cm of starch solution and 1cm of the buffer pH solution in a test tube and start a stopwatch.
4. After 10 seconds, use a pipette to place a drop the solution into one of the wells containing iodine solution. The mixture should turn blue-black to indicate that starch is still present and has not yet been broken down.
5. Repeat this after another 10 seconds.

6.Continue repeating until the solution remains orange, and record the time taken 6. Repeat Steps 1-5 with a buffer solution of different pH.

7. Record your results on a graph of pH (on the x-axis) and time taken to complete reaction (on the y-axis)

Question 28

Why do we use a Bunsen Burner and water beaker in this experiment?

Answer 28

We use this equipment to keep the solution at a relatively constant temperature throughout the reaction (temperature is a control variable in this experiment).

Question 29

What results do we expect to see in this experiment?

Answer 29

The optimal pH of amylase will be at whichever pH the reaction completes in the shortest time. This should be somewhere around pH 7.0.

Question 30

What is the rate calculation?

Answer 30

Rate = change/time

Question 31

What are Carbohydrases?

Answer 31

-Carbohydrases convert carbohydrates into simple sugars

-Example: amylase breaks down starch into glucose and maltose. It is produced in your salivary glands, pancreas and small intestine (most of the starch you eat is digested here)

Question 32

What are proteases?

Answer 32

-Proteases convert proteins into amino acids

-Example: pepsin, which is produced in the stomach, other forms can be found in pancreas and small intestine.

Question 33

What are lipases?

Answer 33

-Lipases convert lipids (fats) into fatty acids and glycerol, produced in the pancreas and small intestine.

Question 34

What is the iodine test for?

Answer 34

-Starch
-Add iodine solution to the food sample. If starch is present, the colour will change from orange to blue-black

Question 35

What is the Benedicts reagent test for?

Answer 35

-Reducing sugars
-Add equal volumes of the sample solution and blue Benedict’s solution to a test tube. Place in a boiling water bath until there is no further change in colour. Presence of reducing sugar is indicated by a colour change to reddish-brown

Question 36

What is the Biuret test for?

Answer 36

-Proteins
-Shake the sample solution and
the biuret solution, well and observe colour change if protein is present (blue —> violet)

Question 37

What is the Ethanol emulsion test for?

Answer 37

-Lipids (fats and oils)
-Add equal volumes of ethanol and water to the food sample and shake thoroughly. if lipids are present, this will be indicated by the formation of a white emulsion layer at the top of the sample.

Question 38

What is Calorimetry?

Answer 38

Calorimetry is a way to measure the energy taken in and given out during a chemical reaction. We can use this to measure the amount of ‘energy’ (calories) in food.

Question 39

What are the steps to a calorimetry experiment?

Answer 39

1 Take a tube of 50ml cold water.

2. Record the starting temperature of the water.
3. Place the test tube at 45 degrees and hold a burning food sample just beneath
4. When the food is burned up, record the final temperature of the water.

Question 40

What is diffusion?

Answer 40

Diffusion- a form of passive transport (does not require energy), the molecules’ net movement is from an area of high concentration to one of low concentration.

Question 41

How can you work out the energy transferred to the water using the equation?

Answer 41

Energy transferred mass of water x 4.2 x temperature increase

Question 42

What is osmosis?

Answer 42

Osmosis is also a form of passive transport (does not require energy) but it only applies to water. The net movement is from a dilute (high water concentration) solution to a more concentrated (low water concentration) solution, across a selectively permeable membrane.

Question 43

What is active transport?

Answer 43

Active Transport is a form of transport that does require energy. Active transport is used to move molecules against a concentration gradient (from an area of low concentration to an area of high concentration).

Question 44

What are the steps to investigating osmosis in potatoes?

Answer 44

1. Cut potato into small discs of equal size (e.g 2cm diameter).
2. Blot the potato disks gently with tissue paper to remove excess water
3. Measure the initial mass of each disk.
4. Place the disks in sucrose solutions of different concentrations (1%, 2% etc)
5. Blot with tissue paper again and record new mass.
6. Find difference in mass (end mass- start mass) and use the percentage change equation to calculate percentage gain or loss of mass.

Question 45

What is the percentage change equation?

Answer 45

The percentage change equation is (change in mass/ start mass) x 100.

Question 46

What are the independent, dependent and control variables in this experiment?

Answer 46

-We are changing the concentration of the sucrose solution so this is the independent variable.

-We are measuring the change in mass of the potato disks, therefore this is the dependent variable

-We are controlling the diameter of the disks therefore this is a control variable

Question 47

What is happening in this experiment?

Answer 47

Water is moving by osmosis from a more dilute solution (in the potato) to a more concentrated solution (the sucrose solution) across a selectively permeable membrane (the cell membranes of all the potato cells holding water)