Page 65 - PRE-U STPM BIOLOGY TERM 1

Biology Term 1 STPM Chapter 2 Structure of Cells and Organelles
• Through the endothelium, oxygen and nutrients • The cell wall is thin, made up of only primary cell
can diffuse out of the blood capillaries while wall.
carbon dioxide and urea can diffuse into them. • The nucleus is large, relative to the volume of the
• Simple cuboidal epithelia are found in the cell.
tubules of the nephron of kidneys. • There is no intercellular space; the cells are compact.
• In the proximal convoluted tubule, their plasma • The protoplasm is dense, with few organelles and
membrane facing the lumen is modified to the organelles are small.
form ultra-villi for reabsorption of molecules. • Apical meristem is found at the shoot and root tips.
2 • In the distal and collecting ducts, the epithelia • Its function is to produce primary tissues, such
form tubule to channel urine though can be as tissues found in a herbaceous plant.
affected by ADH for special water reabsorption. • Vascular cambium is found mainly in woody stems
• Simple columnar epithelia are found in the and roots.
outermost lining of the stomach and intestines. • Its function is to produce secondary xylem (wood)
• These epithelia serve more of protection as and phloem.
their outer surfaces are covered with mucus. • Cork cambium (phellogen) is found on the outer
• In the small intestine, their plasma membranes layer of dicotyledonous woody stems and roots.
have special transport proteins for absorption • Its function is to produce cork cells (phellem) on
of digested food molecules. the outside and secondary cortex (phelloderm) on
4. • Meristem is a group of cells that are able to divide the inside.
and continue to divide. • Intercalary cambium is only found in
• It consists of a group of initial cells that can divide monocotyledons especially Gramineae.
very fast. The cell products will divide at a slower pace. • It is a thin layer of cells above the node of the stem
• After cell division, one of the daughter cells will when it is young. Its function is to produce more
move away and become differentiated while the cells for the internode and will later disappear.
others are retained and continue to divide.
• Therefore, meristem is a localised tissue and tends
to move up for the bottom cells to grow as in the
shoot apical meristem.
• All the cells in the meristem are young and have not
undergone differentiation.
• The cells have isodiametric prismatic shapes.

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