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Specialised cellsIB MYP Biology: Revision notes

Section 1

Structure and function

A specialised cell has a special structure that suits it to its job. When you answer an exam question, link each feature of a cell to its function and explain why it helps.

A good answer uses the pattern: feature, so function. For example: "A red blood cell has no nucleus, so there is more room for haemoglobin."

Key termsspecialised celladaptation

Section 2

Blood cells

Red blood cells carry oxygen from the lungs to the body.

  • Biconcave (dip in the middle) shape: large surface area to absorb oxygen quickly.
  • No nucleus: more room for haemoglobin, the red substance that carries oxygen.

White blood cells protect the body from disease.

  • They can change shape to surround and engulf pathogens (microorganisms that cause disease).
  • They have a nucleus. Some also make chemicals called antibodies.
Key termsred blood cellhaemoglobinwhite blood cellpathogen
Common mistake

Do not say red blood cells are 'round and flat'. The key feature is the biconcave shape, which gives a large surface area.

Section 3

Nerve cells

Nerve cells carry electrical impulses around the body.

  • A very long axon carries the impulse over long distances.
  • Branched endings connect to many other nerve cells.
  • Some have a fatty insulating layer that speeds up the impulse.

The length of the cell means one cell can reach from the spinal cord to a toe.

Key termsnerve cellaxonelectrical impulse

Section 4

Sperm and egg cells

Sperm cells carry the father's genetic information to the egg.

  • A tail to swim to the egg.
  • Many mitochondria to release energy for swimming.
  • Enzymes in the head to digest the outer layer of the egg.
  • A nucleus containing genetic information.

Egg cells carry the mother's genetic information and feed the early embryo.

  • A large cytoplasm with a food store.
  • A nucleus containing genetic information.
  • A membrane that changes after one sperm enters so that no more can enter.
Key termssperm cellegg cellfertilisation

Section 5

Plant cells: root hair, palisade and xylem

Root hair cells absorb water and mineral ions from the soil.

  • A long, thin extension gives a large surface area.

Palisade cells carry out photosynthesis in the leaf.

  • Many chloroplasts to absorb light.
  • Tall and packed close together near the top of the leaf.

Xylem cells carry water and mineral ions up the plant.

  • Hollow tubes with no end walls, so water flows in a continuous column.
  • Walls strengthened with lignin, which supports the plant.
Key termsroot hair cellpalisade cellxylemlignin
Exam tip

Palisade cells are in the leaf, root hair cells are in the root, and xylem runs through the stem. Say where a cell is found as well as what it does.

Must Know

  • Red blood cell: biconcave, no nucleus, carries oxygen
  • White blood cell: changes shape to engulf pathogens
  • Nerve cell: long axon and branched endings
  • Sperm: tail, many mitochondria, enzymes. Egg: food store
  • Root hair: large surface area. Palisade: many chloroplasts. Xylem: hollow tube with lignin

That's the notes covered.

Carry on to the next subtopic.

Exam questions on Specialised cells

  1. A haematologist examines a drop of blood under a microscope. She sees a very large number of small, round cells with a dip in the middle and no nucleus, and a few larger cells that have a lobed nucleus and an irregular outline.
    Explain how two features of red blood cells help them to carry oxygen.2 marks
  2. A botanist studies the cells of a young plant. She identifies palisade cells near the top surface of a leaf, root hair cells on the surface of a root, and xylem vessels carrying water up the stem.
    Explain how the structure of a palisade cell helps it to carry out photosynthesis.2 marks
  3. A student wants to find out whether root hair cells help a plant to absorb water. She sets up two cress seedlings of the same species in identical test tubes of water, with a thin layer of oil on top of the water to stop evaporation. She cuts the bottom 1 cm off the roots of one seedling, which removes its root hairs, and leaves the roots of the other seedling whole. She leaves both for 24 hours.
    State a testable hypothesis for the investigation, with a scientific reason, and identify the independent variable.3 marks
See the full worksheet

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).