Ch 1-4 Flashcards
(21 cards)
Q1 Describe the cellular processes involved in enzyme synthesis and secretion. [6]
The gene that codes for the enzyme undergoes transcription to produce an mRNA molecule in the nucleus;
The mRNA molecule diffuses out of the nucleus into the cytoplasm. There, the mRNA molecule undergoes translation by the ribosomes;
Ribosomes on the rough endoplasmic reticulum (RER) synthesise the polypeptide that makes the enzyme;
The polypeptide is then transported by the RER to the Golgi body;
The Golgi body chemically modifies the polypeptide into a functional enzyme, sorts, and then packs the enzyme into secretory vesicles;
These secretory vesicles then move towards the cell surface membrane, fuse with the cell surface membrane and release the enzyme out of the cell.
Q2 Describe the structural features of a root hair cell and explain how each feature adapts the cell to its function. [4]
A root hair cell has a long and narrow protrusion;
which helps to increase surface area to volume ratio for faster absorption of water by osmosis and mineral salts by active transport and diffusion;
A root hair cell has numerous mitochondria;
to carry out aerobic respiration to release more energy for active transport of mineral salts into the cell;
Q3 Compare the structure of a typical animal and plant cell. [4]
In both a typical animal and plant cell, the nucleus, cytoplasm, and cell surface membrane are present;
The cell wall is present in a plant cell but absent in an animal cell;
Some plant cells contain chloroplast, while all animal cells do not;
Plant cells have a large and centralised vacuole, while animal cells have small and numerous vacuoles;
Q4 Explain why root hair cells, liver cells, muscle cells all have a large number of mitochondria. [5]
mitochondria carry out aerobic respiration to release energy;
for liver cells to produce many enzymes needed for blood glucose regulation / detoxification / deamination of excess amino acids / any 2;;
for muscle cells to contract and relax to enable movement;
for root hair cells to carry out active transport to take in mineral ions from the soil into the cell;
Q5 Explain how red blood cells are adapted to their function. [6]
Red blood cells have a biconcave disc shape;
which increases surface area to volume ratio, to increase the rate of diffusion of oxygen in and out of the cell;
Red blood cells have no nucleus;
for more space to contain more haemoglobin so that more oxygen can be carried in the red blood cell;
Red blood cells contains haemoglobin;
which binds to oxygen reversibly to transport oxygen from the lungs to the rest of the body;
Q6 Compare the processes of active transport, diffusion, and osmosis. [3]
Both diffusion and osmosis involve the net movement of substances down a concentration and water potential gradient respectively while active transport is the net movement of substances against the concentration gradient;
Diffusion and osmosis do not require cellular energy and are passive processes while active transport requires cellular energy;
Osmosis and active transport takes place across a partially permeable membrane while diffusion can occur with or without a partially permeable membrane;
Osmosis involves only water molecules, while diffusion and active transport involves atoms, molecules, and ions of any substances;
Q7 Describe and explain what happens to a plant cell when it is placed in concentrated salt solution for 20 minutes. [4]
The cell sap of the plant cell has a higher water potential than the concentrated salt solution;
The water molecules move out of the cell into the solution through the partially permeable cell membrane by osmosis;
The vacuole decreases in size and the cell becomes flaccid;
After prolonged immersion in the concentrated salt solution, excessive loss of water causes the cytoplasm to shrink away and tear from the cell wall, hence the cell becomes plasmolysed;
Q8 Describe and explain what happens to a strip of potato tuber when it is placed in concentrated sugar solution for 20 minutes. [4]
The strip of the potato tuber becomes softer in texture and shorter in length;
The cell sap of the potato cells has a higher water potential than the concentrated sugar solution;
Therefore, water molecules move from the potato cells into the concentrated sugar solution through the partially permeable cell surface membrane by osmosis;
Water loss causes the cells to become flaccid hence accounting for the loss of firmness and decrease in the length of the potato strip;
Q9 Describe and explain what happens to a strip of potato tuber when it is placed in distilled water for 20 minutes. [4]
distilled water has a higher water potential than the cell sap of potato cells;
water molecules enter the cells of the potato tuber by osmosis;
the vacuole and cytoplasm of the potato cells increases in volume and pushes the cell contents against the cell wall;
hence, the cells become turgid and the potato strip becomes firm and increases in size.
Q10 The cytoplasm of red blood cells contain about 54.8 % to 78.1 % water. Explain what happens when red blood cells are incubated in solutions with water content of less than 54.8% and in distilled water. [4]
The cytoplasm of the red blood cells has a higher water potential than the solution with water content of less than 54.8%, hence water molecules move out of the red blood cell by osmosis;
The cells shrinks and crenates;
The cytoplasm of the red blood cells has lower water potential than distilled water, water molecules move from the distilled water into the red blood cell by osmosis;
The cell swells and bursts/lyses;
Q11 Name the components of a balanced diet and for each component, state the role(s) of the component in living organisms. [6]
The components are carbohydrates, proteins and fats;
glucose is used as a substrate for respiration to release energy for cellular processes;
protein is used to synthesise enzymes that are biological catalysts which can speed up the rate of biochemical reactions by lowering activation energy;
protein is used to synthesise the protoplasm of cells for cell growth and tissue repair;
fat and protein can be used to synthesise hormones, which are chemical signals that coordinate physiological processes in the body;
subcutaneous fat under the skin insulates the body against excessive heat loss;
visceral fat around internal organs to provide mechanical protection for internal organs;
fats are dense in calories, fats are stored as a long-term storage of energy;
any 6 ;;;;;;
Q12 Describe how would you test a solid sample for the presence of protein. [2]
Add 2ml of biuret reagent to 2g of the crushed solid sample in a clean test tube +
Shake vigorously to mix well;
If protein is present, the blue biuret reagent turns violet. If protein is not present, the biuret reagent remains blue;
Q13 Describe the procedure to carry out the ethanol emulsion test on solid samples. [4]
Add 2ml of ethanol to 2g of crushed solid sample into a clean test tube;
and shake vigorously;
Decant supernatant into a clean test tube with 2ml of distilled water;
If the mixture remains clear, fats are absent. If the mixture forms a white emulsion, fats are present;
Q14 Outline the steps to test for the presence of reducing sugars in solid samples. [4]
add 2g of crushed solid samples into a test tube with 2ml of Benedict’s solution;
shake the test tube vigorously;
put the test tube into the boiling water bath and wait for 5 minutes;
after 5 minutes, if red/orange/yellow precipitate forms, reducing sugars are present. if the Benedict’s solution remains blue, reducing sugar is absent;
Q15 Outline the steps to test for the presence of starch in solid samples.
[2]
Add 2 drops of iodine solution to 2 g of crushed solid samples ;
If starch is present, brown iodine solution turns blue black. If starch is absent, iodine solution remains brown;
Q16 Milk contains fat. Phenolphthalein is an indicator that is pink in alkaline conditions above pH 8 and becomes colourless when the pH drops below 8. Milk, lipase, and phenolphthalein were stirred together to form a mixture. Sodium carbonate was added to this mixture to make the solution alkaline, hence the mixture turned pink once sodium carbonate was added in. After 20 mins, the mixture became colourless. Explain why. [3]
Lipase digests fat in the milk into fatty acids and glycerol;
fatty acids are acidic and will neutralise the effect of sodium carbonate in the mixture;
when fatty acids are produced in excess, pH drops below 8, causing phenolphthalein in the mixture to turn from pink to colourless;
Q17 Describe the mode of action of enzymes. [6]
The shape of the substrate is complementary to the shape of the active site of the enzymes;
hence enzymes are specific in action;
the substrate then binds the active site of the enzyme, forming the enzyme-substrate complex;
which allows the enzyme to catalyse the biochemical reaction and increase the rate of reaction by lowering the activation energy of the reaction;
once products are formed, they are released from the active site of the enzyme;
enzyme remains chemically unchanged and are free to bind itself to new substrates hence enzymes are only needed in minute amounts;
Q18 Using the lock and key hypothesis, explain why amylase digests starch but not proteins. [5]
The lock and key hypothesis likens the enzyme to a lock, and the substrate to a key;
The shape of the active site of amylase is complementary to the shape of the starch molecule;
so that starch can fit into the active site of amylase and form the enzyme-substrate complex for amylase to catalyse the hydrolysis of starch by lowering the activation energy of the reaction;
Hence, enzymes, like amylase, are specific in action;
However, the shape of protein and the shape of the active site of amylase are not complementary, so amylase is unable to catalyse the reaction and cannot digest protein;
Q19 Describe the properties of enzymes. [6]
Enzymes are biological catalysts that speed up the rate of biochemical reaction by lowering the activation energy;
Enzymes are proteins in nature;
Enzymes remain chemically unchanged at the end of a biochemical reaction, so it can be reused and thus enzymes are required in minute quantities;
Enzymes are specific in action;
Only a substrate that is complementary to the shape of the active site of the enzyme can fit into the active site of the enzymes to form an enzyme-substrate complex for catalysis to occur;
Enzymes are inactive at low temperatures and denature at high temperatures;
Enzymes denature at extreme pH;
Any 6;
Q20 Explain how extreme pH affects enzyme activity. [4]
The extremely high and low pH would disrupt the intramolecular bonds of the enzyme molecules;
This would change the shape of the active site of the enzyme;
causing the enzyme to be denatured;
Substrate is no longer able to fit in the active site of the enzyme and enzyme is unable to catalyse the reaction;
Q21 Explain the effect of increasing temperature on the rate of enzymatic reaction. [4]
When the temperature is low, the rate of enzyme-catalysed reaction is low because the enzymes are inactive;
As temperature increases, the rate of reaction increases gradually because the kinetic energy of the enzyme and substrate molecules will increase, causing the probability of effective collision between the enzyme and substrate molecules to increase. Hence, the frequency of formation of enzyme-substrate complex increases;
At the optimum temperature, the rate of reaction reaches the maximum;
As the temperature increases beyond the optimum temperature, the rate of reaction decreases drastically to zero because high heat energy disrupts the intramolecular bonds of the enzyme, causing a change in the shape of the active site. Hence, the substrate can no longer fit into the active site and the enzyme is denatured;
