Chapter 2
Answers
1
QUICK-CHECK questions
What is meant by the label ‘partially permeable’ in reference to the plasma
membrane?
The label ‘partially permeable’ refers to a barrier that allows the passage of some, but
not all, dissolved materials. The plasma membrane of a cell has this property.
2
Which of the following is an energy-requiring process?
a
osmosis
b
diffusion
c
active transport
d
facilitated diffusion
Of these four processes, only (c), active transport, is an energy-requiring process.
During active transport, dissolved substances are moved against a concentration
gradient: that is, from a region of low concentration to a region of higher concentration.
In contrast, during osmosis and during diffusion and facilitated diffusion, substances
move from a region of higher concentration to one of lower concentration.
3
What is the function of a cell wall?
The cell wall, a semi-rigid structure found in the cells of plants, bacteria and fungi,
provides support to these cells.
4
True or false? Briefly explain your choice.
a
A nucleus from a plant cell would be expected to have a nuclear envelope.
True: In all eukaryotic cells, including plant cells, the nucleus is enclosed within a
double membrane known as the nuclear envelope.
b
Bacterial cells do not have DNA.
False: Bacterial cells contain DNA as their genetic material.
c
A mature red blood cell is an example of a prokaryotic cell.
False: A mature blood cell is an example of a eukaryotic cell. It is, however, an
atypical example, since mature red blood cells do not have a nucleus, but, earlier
in their lives, immature red blood cells have the membrane-bound nucleus that is
characteristic of eukaryotic cells.
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Suggest why the nucleus is called ‘the control centre’ of a cell.
The nucleus may be termed ‘the control centre’ of a cell since it is the site of the DNA
that contains the genetic instructions that determine the structural, biochemical and
physiological properties of a cell.
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Chapter 2: QUICK-CHECK answers
6
Is the major site of ATP production the same in a plant cell as in an animal cell?
The major site of ATP production in both plant and animal cells is the mitochondrion.
7
A scientist wishes to examine ribosomes in pancreatic cells.
a
Where should the scientist look — in the nucleus or in the cytoplasm?
To examine ribosomes in pancreatic cells (and indeed in any cell type), a scientist
should look in the cytoplasm of the cells.
b
What kind of microscope should the scientist use?
Because ribosomes are below the resolution of a light microscope, they need to
be viewed using a transmission electron microscope (TEM).
8
A substance made in a cell is moved outside the cell. Outline a possible pathway
for this substance.
Assuming that the substance made within a cell is a protein, it is reasonable to suggest
that the substance would be produced on the ribosomes. It would be transported within
the cell via the channels of the endoplasmic reticulum and then transported out of the
cell through the Golgi complex. In summary:
ribosomes  endoplasmic reticulum  Golgi complex  outside of cell
9
Lysosomes are sometimes called ‘suicide bags’. Suggest why this name is
given.
Lysosomes are sometimes called ‘suicide bags’ because they contain dissolved
digestive enzymes that, when released, can cause the death of a cell.
10
Identify the following as true or false and briefly justify your answers.
a
Plant cells without chloroplasts can capture the energy of sunlight.
False: The cell organelles that are essential for the capture of the energy of
sunlight are the chloroplasts.
b
Chloroplasts can be seen through an LM.
True: Chloroplasts are sufficiently large that they can be seen using a light
microscope (LM).
11
List one location in the human body where cells with cilia are found.
Cells with cilia are found in several locations within the human body, including the
trachea.
12
Consider a cell with cilia beating on its surface. Identify one other organelle that
would be expected to assist in the action of these cilia.
Because the beating of cilia is an energy-requiring process of a cell, it is reasonable to
suggest that mitochondria would be present to assist the action of the cilia.
Mitochondria are the cell organelles that are the major site of production of ATP, the
energy source for cells.
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Chapter 2: QUICK-CHECK answers
13
List four cell organelles that are involved in the process of making protein. What
is the contribution of each organelle to this process?
Four cell organelles involved in the process of making protein are:
 Nucleus: contains the instructions for making each specific protein
 Ribosome: the site where the amino acid sub-units are joined into a
polypeptide/protein chain
 Mitochondrion: the site production of ATP, which supplies the energy necessary to
build protein chains
 Endoplasmic reticulum: transports newly synthesised proteins away from the
ribosomes.
14
Does an amoeba have organs? Explain.
No. An amoeba is a unicellular organism. Organs are structures made of groups of
different tissues that are made of cells. So, a single-celled organism, such as an
amoeba, cannot have organs.
15
What characterises a tissue, an organ and an organ system?
A tissue consists of a group of similar cells that carry out a particular function.
An organ consists of various tissues that together carry out particular functions.
An organ system consists of a group of organs that work together to perform a major
function, such as digestion or excretion.
16
Classify each of the following as tissue, organ or system.
 nerve cells in the tip of a finger
Nerve cells at a fingertip are similar cells carrying out the same function and so they
form a tissue.
 fleshy part of an apple
The fleshy part of an apple is made up of similar cells with the same function and
so it is a tissue. This edible fleshy part of an apple is the so-called mesocarp tissue.
 a flower
A flower contains various plant reproductive tissues and so a flower is an organ.
 nose, trachea and lungs
The nose, trachea and lungs are individual organs that are part of the respiratory
system.
 a human liver
The human liver consists of various tissues that work together to perform various
functions. So, the liver is an organ.
 layer of fat around a kidney
The layer of fat around a kidney consists of similar cells that perform the same
function. So, the fat layer is a tissue.
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