Page 39 - PRE-U STPM BIOLOGY TERM 1

Biology Term 1 STPM Chapter 2 Structure of Cells and Organelles

Learning Outcomes 2.3 Specialised Cells

Students should be able to:
(a) outline the structures,
functions and 1. Specialised cells are cells that have undergone specialisation or
distributions of differentiation in the course of embryonic development. All cells
unspecialised cells
found in plants of a multicellular organism develop from a single zygotic cell after
(meristematic cells); fertilisation. Since then, mitosis increases the cell number and
2 (b) describe the
structures, functions ensures exact genetic makeup in all the cells formed later. However,
and distributions of in the course of development, cells acquire different structures and
specialised plant cells
found in epidermal, functions.
ground and vascular
tissue; 2. Specialisation is a result of genes being ‘switched on’ or ‘switched
(c) describe the off’ during development, even though the cells have the same genetic
structures, functions
and distributions of content for a particular individual.
specialised animal cells
found in connective, 3. Red blood cells have their haemoglobin genes ‘switched on’ when
nervous, muscular they were developed in the bone marrow, but their melanin genes
and epithelial tissues,
including the formation are ‘switched off’. Conversely, skin cells have their haemoglobin
of endocrine and genes ‘switched off’ whereas their melanin genes ‘switched on’ in the
exocrine glands.
course of development.

Unspecialised Cells Found in Plants

Meristematic cells
Exam Tips 1. Meristematic cells are cells found in the meristem, a localised tissue
Remember the eight basic that can divide by mitosis.
plant tissues.
2. The structures of meristematic cells are as follows:
(a) All the cells are young and have not undergone differentiation.
They look the same and have the same size.
Summary (b) Apical meristematic cells have isodiametric prismatic shapes.
They are all regular in shape and almost look spherical.
Unspecialised cells in Cambium cells are brick-like and some are very thin.
plants (meristematic cells) (c) The cell wall is thin, only made up of primary cell wall. The cells
Thin wall, little cytoplasm
and compact can be easily damaged and nutrients can easily diffuse into them.
1. Apical meristem – found (d) The nucleus is large, relative to the volume of the cell. All the
at tips of shoot and root nuclei are ready to start mitosis.
to form primary tissues
2. Vascular cambium (e) There is no intercellular space; the cells are compact and are
– found in vascular close together.
bundle woody plants to (f) The cytoplasm is dense, with few organelles which are small.
form secondary xylem
and phloem All the organelles are young. Chloroplasts if present, are in the
3. Cork cambium – found proto-plastid stage.
beneath epidermis
of woody dicots to 3. The distributions and functions of meristem are as follows:
produce cork
4. Intercalary cambium (a) Apical meristem. It is found in the shoot and root tips. Its
– found in grasses to function is to produce primary tissues, such as tissues found in a
produce cells above herbaceous plant.
nodes
(b) Vascular cambium. It is found mainly in woody stems and

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