Page 140 - Biology_F5

Comparative studies of natural groups of organisms

moist. They are unicellular, and they lack are found within the cytoplasm (Figure
hypha. They have eukaryotic organelles 3.20). The cell walls of Saccharomyces are
such as mitochondria, ribosomes, Golgi elastic, determine the shape of the cell, and
apparatus, vacuoles and ribosomes which provide osmotic and physical protection.

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Scar of attachment Cell wall
to parent cell Vacuole
Cytoplasm
Nucleus Cytoplasm

Cell membrane
Chitin cell wall Nucleus
Mitochondrion Food reserves such
New cells attached
Vacuole to parent cell as glucose and oil

(a) (b)

Figure 3.20: Structure of Saccharomyces (a) a single cell (b) a budding cell

Adaptations of Saccharomyces to its (e) Spores’ ability to remain dormant in
mode of life unfavourable conditions ensures their

Saccharomyces species have the following survival.
adaptive features that enable them to suit (f) Some Saccharomyces are facultative
to their mode of life: anaerobes. They have ability to respire
anaerobically and aerobically. This
(a) They store carbohydrates in the form ensures survival under both aerobic
of glycogen for use during food and anaerobic conditions.
shortage.
(b) They have permeable cell walls to allow
entry of nutrients that are obtained Activity 3.4: Observation of yeast
from external digestion. Thus, they cells under light microscope
can absorb simple monosaccharides
and vitamins directly from their Materials
environment. Yeast cells, water, beaker, stirring rod,
(c) They secrete extracellular enzymes dropper, slides, and microscope
such as sucrase and cellulase for
digestion of carbohydrates, and Procedure
protease for digestion of proteins. (a) Put some yeast in a beaker contain-
(d) They have high reproductive rate ing small amount of water, then stir
through budding, hence abundant in to get a suspension.
number.

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