Specialised cells and organisation — answer key

1. OQ1 · Practice

Options as numbered on the pupil sheet: 1 — Moves mucus in the trachea and bronchi; 2 — Absorbs water and mineral ions; 3 — Photosynthesis; 4 — Conducts electrical impulses; 5 — Transports oxygen; 6 — Reproduction.

Model answer. Ciliated cell: moves mucus in the trachea and bronchi. Root hair cell: absorbs water and mineral ions from the soil. Palisade mesophyll cell: photosynthesis. Neurone: conducts electrical impulses. Red blood cell: transports oxygen. Sperm and egg cells (gametes): reproduction.

A full answer includes

• Ciliated cell → moves mucus in the trachea and bronchi.
• Root hair cell → absorbs water and mineral ions.
• Palisade cell → photosynthesis.
• Neurone → conducts electrical impulses.
• Red blood cell → transports oxygen.
• Sperm and egg cells → reproduction.

Also accept

• ciliated–mucus; root hair–absorption; palisade–photosynthesis; neurone–impulses; red blood cell–oxygen; gametes–reproduction.

Watch for

• “Root hair cells photosynthesise.” — They are in the dark soil and have no chloroplasts; their job is absorbing water and mineral ions.
• “Cilia help the cell swim.” — Ciliated cells in the airways stay in place; their cilia sweep mucus along. A sperm swims with its tail.

2. OQ2 · Practice

Model answer. c. New cells are produced by the division of existing cells. Each new cell gets a copy of the genetic material.

A full answer includes

• I chose c: by division of existing cells.

Also accept

• c; existing cells divide.

Watch for

• “Cells form from the food we eat.” — Food supplies materials and energy, but a new cell always comes from an existing cell that divides.
• “The nucleus makes new cells.” — The nucleus holds the genetic material, which is copied; then the whole cell divides into two.

3. OQ3 · Practice

Options as numbered on the pupil sheet: 1 — Organ; 2 — Cell; 3 — Organism; 4 — Tissue; 5 — Organ system.

Model answer. Cell → tissue (a group of similar cells working together) → organ (a group of tissues working together) → organ system (a group of organs with related functions) → organism.

A full answer includes

• cell, tissue, organ, organ system, organism.

Also accept

• cell, tissue, organ, organ system, organism

Watch for

• “An organ is smaller than a tissue.” — An organ is made of several tissues, so it is a larger level.

4. OQ4 · Practice

Model answer. Any two of: a red blood cell is full of haemoglobin, the substance that carries oxygen; it has no nucleus, so there is more room for haemoglobin; its flattened disc shape gives a large surface for oxygen to enter and leave.

A full answer includes

• I gave two features, each with how it helps. Any two of: it is full of haemoglobin, which carries oxygen; it has no nucleus, so there is more room for haemoglobin; its flattened disc shape gives a large surface for oxygen to pass in and out.

Also accept

• any two of: haemoglobin carries oxygen; no nucleus = more space for haemoglobin; disc shape = large surface.

Watch for

• “It has no nucleus so it is not a real cell.” — It is a cell specialised for one job; losing its nucleus makes room for more haemoglobin.

5. OQ5 · Practice

Options as numbered on the pupil sheet: 1 — Cell; 2 — Tissue; 3 — Organ; 4 — Organ system; 5 — Organism.

Model answer. One root hair cell is a cell. A layer of many similar ciliated cells is a tissue. The heart is an organ: muscle tissue, a lining and other tissues work together in it. The heart, blood vessels and blood together form an organ system (the circulatory system). A rabbit is a whole organism.

A full answer includes

• One root hair cell → cell.
• A layer of ciliated cells lining the trachea → tissue.
• The heart → organ.
• The heart, blood vessels and blood working together → organ system.
• A rabbit → organism.

Also accept

• root hair cell–cell; ciliated layer–tissue; heart–organ; heart + vessels + blood–organ system; rabbit–organism.

Watch for

• “The heart is an organ system, because it is so important.” — Importance is not the test. The heart is one organ made of several tissues; with the blood vessels and blood it belongs to an organ system.
• “A layer of ciliated cells is an organ.” — It is many cells of the same kind doing one job, so it is a tissue.

6. OQ6 · Practice

Model answer. (a) The cells with dark threads (chromosomes) are dividing: each has copied its genetic material and is splitting into two new cells. (b) The tip is where the root grows. Growing needs new cells, and every new cell comes from an existing cell that divides, so some cells there are always dividing.

A full answer includes

• (a) They are dividing: the genetic material has been copied and is being pulled apart, so each cell becomes two.
• (b) The root tip is growing. Growth needs new cells, and new cells are made only by the division of existing cells.

Also accept

• (a) dividing (making two new cells); (b) the root is growing: new cells come only from division of existing cells.

Watch for

• “The dark threads show that the cells are dying.” — The threads are chromosomes, packed tightly while a cell divides. They show new cells being made.
• “A root grows because its cells take in food and turn it into new cells.” — Food supplies materials and energy, but each new cell is made when an existing cell divides.

7. OT1 · Apply

Model answer. (a) They absorb digested food (small, soluble molecules) from the gut. The tiny projections give a much larger surface area, so more molecules can pass into the cells in the same time, like the long extension of a root hair cell. (b) The layer is a tissue: many cells of the same kind working together. The intestine, with several tissues, is an organ.

A full answer includes

• (a) Their job is absorbing (digested food molecules); the folds give a much larger surface area, so more can be absorbed at the same time.
• (b) A tissue: many similar cells working together.

Also accept

• (a) absorption; larger surface area means more absorbed at once; (b) tissue.

Watch for

• “The folds make the cell stronger.” — Folds of the cell surface increase its area for absorption; strength is not their job.