Section 1: Cells, membranes and DNA

Name the process and its direction: diffusion and osmosis go down a concentration gradient, active transport against it and needs energy. Say which concentration is higher.

A lesson for this section

Multiple choice, Section 1 style

Question 1

In which structure of a cell are proteins assembled from amino acids?

Question 2

The flight muscles of a hummingbird contract many times every second. Compared with a skin cell, which structure would you expect a flight muscle cell to contain in far greater numbers?

Question 3

Which list contains only structures found in a typical bacterial cell?

Question 4

Yeast is a fungus. Which statement correctly compares a yeast cell with a typical leaf cell?

Question 5

Structures present in cells W, X, Y and Z.
Structure	Cell W	Cell X	Cell Y	Cell Z
Cell wall	cellulose	absent	not cellulose	not cellulose
Nucleus	present	present	absent	present
Chloroplasts	present	absent	absent	absent
Plasmids	absent	absent	present	absent

The table shows some structures in four cells, W, X, Y and Z. Which cell is a fungal cell?

Question 6

What is a plasmid?

Question 7

What is the function of the cell wall in a plant cell?

Question 8

A student looks at cells from the inside of an onion bulb under a microscope. The cells have no chloroplasts. Which feature shows that they are plant cells rather than animal cells?

Question 9

What is the function of the nucleus?

Question 10

In which part of a cell do most of the chemical reactions take place, including the first stage of respiration?

Question 11

A student measured the length of five cheek cells under a microscope: 58 µm, 62 µm, 55 µm, 64 µm and 61 µm. What is the average length of these cells?

Question 12

A cell from a moss leaf is 90 µm long and 36 µm wide. What is the simple whole number ratio of its length to its breadth?

Question 13

Which two substances make up the cell membrane?

Question 14

The cell membrane is selectively permeable. What does this mean?

Question 15

A muscle cell is respiring aerobically. How does carbon dioxide move between the cell and the blood around it?

Question 16

An amoeba is a single-celled organism living in pond water that is rich in oxygen. How does oxygen enter the amoeba?

Question 17

Which statement about diffusion and osmosis is correct?

Question 18

A drop of blood is added to pure water. What happens to the red blood cells?

Question 19

Cells from a red onion are left in a concentrated salt solution for 20 minutes. Which describes the cells?

Question 20

Why does a plant cell placed in pure water become turgid instead of bursting?

Question 21

The concentration of nitrate ions inside a root hair cell is higher than in the soil water around it, yet the cell keeps taking in nitrate ions. Which process is it using?

Question 22

A chemical stops the mitochondria in a cell from working, so no energy is released by aerobic respiration. Which process would stop?

Question 23

A potato cylinder had a mass of 2.50 g. After an hour in a sugar solution its mass was 2.20 g. What was the percentage change in its mass?

Question 24

Potato cylinders were left in sucrose solutions of different concentrations for two hours. The graph shows the percentage change in their mass. Which solution has the same water concentration as the potato cells?

Question 25

A student fills a bag of Visking tubing with a solution of starch and glucose, stands it in a beaker of water and tests the water for glucose after 30 minutes. Which control would show that any glucose in the water came from the bag?

Question 26

A student removes the shell from an egg by soaking it in vinegar, then measures its change in mass in syrup. How could the student make the results more reliable?

Question 27

Which describes the structure of a DNA molecule?

Question 28

What is a gene?

Question 29

One strand of a section of DNA has the base sequence A C G T T A G C. What is the sequence of bases opposite it on the other strand?

Question 30

A section of DNA contains 2000 bases in total, of which 240 are thymine. How many cytosine bases does it contain?

Question 31

What is the role of messenger RNA (mRNA) in making a protein?

Question 32

Which sequence shows the route of the genetic code in making a protein?

Question 33

The base sequence of a gene is altered. Which feature of the protein it codes for may be changed as a result?

Question 34

Each amino acid in a protein is coded for by a group of three bases. A section of a gene that codes for the amino acids of a protein is 1500 bases long. How many amino acids does it code for?

Question 35

Which statement about chromosomes and genes is correct?

Question 36

Which structure is found in plant, animal, fungal and bacterial cells?

Question 37

Which structure in a leaf cell absorbs light energy for photosynthesis?

Question 38

A single cell found in a soil sample is known to be one of four kinds: plant, animal, fungal or bacterial. It has a cell wall that is not made of cellulose, it contains mitochondria, and it has no chloroplasts. What kind of cell is it?

Question 39

A cell in rhubarb epidermis is 0.15 mm long and 45 µm wide. What is the simple whole number ratio of its length to its breadth?

Question 40

Uptake of iodide by kelp pieces under three conditions.
Condition	Iodide uptake (units per hour)
Seawater with oxygen bubbled through	48
Seawater with no oxygen	5
Seawater with oxygen, plus a chemical that stops mitochondria working	4

The concentration of iodide ions inside the cells of a kelp seaweed is thousands of times higher than in the seawater around it. Pieces of kelp were kept in seawater under three conditions and their uptake of iodide was measured. Which conclusion do the information and results support?

Question 41

Colour of the water after beetroot discs were left in it for 30 minutes.
Temperature (°C)	Colour of water (units)
20	0.06
40	0.09
60	0.58
80	0.94

Beetroot cells hold a red pigment. Discs of beetroot were rinsed, then left in water at different temperatures for 30 minutes, and the colour of the water was measured. Which explains the large rise in colour between 40 °C and 60 °C?

Question 42

One strand of a section of DNA contains 120 adenine, 80 thymine, 150 cytosine and 50 guanine bases. How many guanine bases are there in the whole double-stranded section?

Question 43

A change in one base of the gene for an enzyme means the cell still makes the enzyme, with the same number of amino acids, but the enzyme no longer works. Which explanation is correct?

Theory and practical questions

Four kinds of cellSection 2 style · 5 marks

A student uses a microscope and diagrams to compare four cells: a leaf cell, a cheek cell, a yeast cell and a bacterial cell. The table shows whether some structures are present in each, numbered 1 to 4.

Structures present in cells 1 to 4.
Structure	Cell 1	Cell 2	Cell 3	Cell 4
Cell wall	cellulose	absent	not cellulose	not cellulose
Nucleus	present	present	present	absent
Chloroplasts	present	absent	absent	absent
Plasmids	absent	absent	absent	present

(a) Which cell is the bacterial cell? [1]

(b) Name the structure in which aerobic respiration is completed. [1]

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(d) State the function of the nucleus. [1]

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Cells in salt solutionsSection 2 style · 7 marks

A student places red blood cells and onion epidermis cells in three solutions: pure water, 0.9% salt solution and 5% salt solution. After 30 minutes the cells are viewed under a microscope. Red blood cells in the 0.9% salt solution have kept their normal shape.

(a) What has happened to the red blood cells in the 5% salt solution? [1]

(b) Name the process by which water moves into and out of the cells. [1]

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(d) Explain why red blood cells burst in pure water but onion cells do not. [3]

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From gene to proteinSection 2 style · 7 marks

A scientist studies the DNA of a mushroom. In a sample of its DNA, 18% of the bases are thymine. In a gene, each amino acid is coded for by a group of three bases.

(a) Calculate the percentage of the bases in the sample that are guanine. [1]

(b) One gene codes for a protein of 240 amino acids. Calculate the number of bases needed to code for these amino acids. [1]

bases

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(d) Describe how the base sequence of a gene is used to make a protein. [4]

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Osmosis in potato cylindersExperiment question · 7 marks

A student investigated the effect of sucrose concentration on the mass of potato tissue. Cylinders were cut from a potato with a cork borer, blotted dry and weighed. Each cylinder was placed in a different sucrose solution. After two hours each was blotted dry and weighed again. The table shows the results.

Mass of potato cylinders before and after two hours in sucrose solutions.
Sucrose concentration / mol per litre	Mass at start / g	Mass after two hours / g	Change in mass / %
0	2.50	2.80	+12.0
0.2	2.40	2.52	+5.0
0.4	2.60	2.60	0.0
0.6	2.50	2.30	−8.0
0.8	2.40	2.10	?

(a) State the independent variable in this investigation. [1]

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(b) Suggest two variables that should be kept the same. [2]

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(d) Explain why the student compared the percentage change in mass rather than the change in mass. [1]

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(e) Write a conclusion for this investigation. [1]

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(f) Describe how the student could make the results more reliable. [1]

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