1.
3 Cell Specialization
Think back
After this topic, you will be able to:
Explain what a specialized cell is.
Name two examples of specialized animal cells and explain how phloem and xylem
cells are adapted to their function.
Name two examples of specialized plant cells.
Unlike unicellular organisms where a single cell can perform all the functions of
life, multicellular organisms contain many cell types. Some specialized cells work
on their own; others work as part of a group.
Key idea
Cells in multicellular organisms are adapted to their function. This makes them
specialized. Xylem and phloem cells are specialized plant cells. They form tissue
that transports materials around a plant.
How do specialized cells differ?
If you look carefully at a specialized cell, its shape and adaptations (special
features) can provide clues about what it does. For example, the sperm cells in
Figure 1 have a tail that enables them to swim towards the egg cell. You can also
see the jelly layer around the egg, which protects the egg cell and attracts sperm.
Together, these adaptations increase the chances of an egg being fertilized and a
baby being produced.
Key words
specialized cell, adaptation, sperm cell, egg cell, muscle cell, xylem, phloem
How do specialized cells work together in animals?
Muscle cells are specialized cells that can contract (get shorter) and relax. These
cells work together in tissues called muscles. For example, antagonistic muscles
work in pairs - one muscle contracts and another muscle relaxes to move the bones
of the skeleton. You can see how muscle cells make up muscle tissue in Figure 2.
Muscle cells have three main adaptations:
[Figure 1
Sperm cells swimming towards an egg cell] They contain proteins that move over
each other to make the fibers contract.
They have many mitochondria to transfer the energy needed to move the proteins.
They store glycogen, which can be broken down into glucose for respiration.
Figure 2 Muscle tissue consists of many muscle cells.
How do specialized cells work together in plants?
Plants contain two types of transport tissue: xylem and phloem. These tissues
transport materials around the plant in tubes.
Xylem tissue
Xylem tissue carries water and minerals from the roots to the rest of the plant. It
is made up of xylem cells. You can see these cells in Figure 3. They have two main
adaptations:
They form long, hollow (empty) tubes. A special chemical called lignin builds up in
the cell wall of xylem cells. The cells then die, forming tubes. This allows water
to move through the tissue easily.
The lignin spirals (coils) also make the tubes very strong. This helps support the
plant stem.
Summary questions
Copy and complete the sentences:
Phloem/Xylem cells transport water in long, hollow/sieve tubes.
Phloem/Xylem cells have hollow/sieve plates to enable dissolved minerals/nutrients
to move freely along the tubes.
Plants contain xylem tissue. Describe the other type of transport tissue plants
contain.
Phloem tissue
Phloem tissue is made up of phloem cells. It transports sugars made by
photosynthesis around the plant. The sugars dissolve, or mix, in water. The
dissolved sugars can then move both up and down the phloem tubes to where they are
needed. Figure 4 shows phloem cells. They have various adaptations:
Sections of the cell walls between the phloem cells break down, forming gaps. These
sections are called sieve plates. These allow dissolved nutrients to move freely
along the tube.
Much of their internal structure is lost to make more space for transport. To keep
the phloem cells alive, they are supported by companion cells. The companion cells
contain mitochondria to transfer the energy needed to move the dissolved food.
3. Phloem and xylem tissue both transport materials around the plant.
Describe two similarities they have.
Describe three differences they have.
4. Explain why unicellular organisms do not contain specialized cells.
5. Explain how muscle cells are adapted to allow muscle tissue to contract and
relax.
6. Explain how phloem cells are adapted to their function.
Figure 3 Xylem cells
Figure 4 Phloem cells░
