Download 2.2 Cell membranes – Questions and answers Q1. Bk Ch2 S2.2 Q1

2.2 Cell membranes – Questions and answers
Q1.
Bk Ch2 S2.2 Q1
a
b
Explain the difference between organic and inorganic substances.
Complete the following table summarising the major groups of organic compounds found in
living things.
Organic compound
Elements
Function
Carbohydrates
Proteins
Lipids
Nucleic acids
A1.
Bk Ch2 S2.2 A1
a
Organic substances always contain carbon atoms and include the major groups of compounds
found in cells, that is, the carbohydrates, lipids, proteins and nucleic acids. Inorganic substances
do not usually contain carbon atoms.
b
Organic
compound
Elements
Function
Carbohydrates
Carbon, hydrogen,
oxygen
Important source of energy for cells. Some
carbohydrates have a structural role, for
example, cellulose that makes up the cell wall of
plant cells.
Proteins
Carbon, hydrogen,
oxygen, nitrogen
Important in the structure of body tissues and
needed for growth and repair
Lipids
Carbon, hydrogen,
oxygen
Make up part of the structure of cell membranes;
energy reserve stored as fat or oils
Nucleic acids
Carbon, hydrogen,
oxygen, nitrogen,
phosphorus
Make up the structure of chromosomes in the
nucleus; important in heredity
Q2.
Bk Ch2 S2.2 Q2
Describe the fluid mosaic model of the cell membrane.
A2.
Bk Ch2 S2.2 A2
The fluid mosaic model of the cell membrane is represented by two layers of special lipids called
phospholipids. The two layers that make up the cell membrane are referred to as a phospholipid
bilayer. Embedded within the bilayer are proteins, some of which span the entire bilayer, as well as
some other molecules. The structure of this model allows for the passage of materials across the
membrane through passive and active means.
Q3.
Bk Ch2 S2.2 Q3
A key role of cell membranes is to regulate the passage of materials into and out of cells. The feature of
cells that allows for this regulatory role is the selectively permeable cell membrane. What is meant by
‘selectively permeable’?
2.2 Cell membranes QA
Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd)
page 1 of 3
A3.
Bk Ch2 S2.2 A3
Selectively permeable refers to the property of cell membranes whereby some kinds of molecules are
able to pass across by simple diffusion while the cell membrane is impermeable to other kinds of
molecules.
Q4.
Bk Ch2 S2.2 Q4
a
b
Distinguish between the processes of diffusion, osmosis and active transport. Use diagrams to
illustrate your answer.
List the substances that move across cell membranes by each of these different processes.
A4.
Bk Ch2 S2.2 A4
a
Diffusion is the process in which molecules passively move from an area of high concentration to
an area of lower concentration.
Osmosis is a special kind of diffusion in which water molecules pass across a selectively
permeable membrane from a dilute to a more concentrated solution.
Active transport is a means by which certain kinds of molecules are carried across the cell
membrane by specialised carrier proteins. This would occur for molecules moving against a
concentration gradient or those that are too large to pass across the cell membrane or cannot
dissolve in it. Active transport requires the expenditure of energy by the cell.
b
Diffusion: simple sugars, some ions, dissolved oxygen and carbon dioxide.
2.2 Cell membranes QA
Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd)
page 2 of 3
Osmosis: water.
Active transport: ions that are needed by cells in concentrations that are higher than the
surrounding tissue fluid, large molecules.
Q5.
Bk Ch2 S2.2 Q5
What is ‘facilitated diffusion’?
A5.
Bk Ch2 S2.2 A5
Facilitated diffusion is a passive process in which cells move substances down a concentration gradient
using carrier proteins in the cell membrane.
Q6.
Bk Ch2 S2.2 Q6
a
b
What is meant by ‘surface area to volume ratio’?
Cells have a large surface area to volume ratio. Explain why this is important for cells.
A6.
Bk Ch2 S2.2 A6
a
b
‘Surface area to volume ratio’ refers to the amount of area covered by the surface of an object
compared to the volume it contains. It is the relationship between an object’s surface area and its
volume. In general, when an object increases in size its volume increases at a faster rate than its
surface area.
It is important for cells to have a large surface area compared to their volume because this allows
for maximum and more efficient exchange of nutrients and wastes between the cell and the
surrounding tissue fluid.
2.2 Cell membranes QA
Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd)
page 3 of 3