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Pearson IB Biology Answers
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ANSWERS,Answers
Chapter 1 Answers are not provided for questions that require individual research or practice.
Exercises
1 As the surface area to volume ratio decreases, between cells can occur, thus bringing about
there is relatively less membrane surface to allow sexual reproduction.
the exchange of wastes between the inside and
7 The area just outside the cell wall of bacteria
outside of the cell. The surface area increases
contains proteins, long-chain polysaccharides,
much more slowly than the volume when the
and lipids that allow the bacteria to stick to the
diameter of a cell increases. Thus, the relative
tooth surface.
amount of membrane available for exchange is
less. If a cell grows too large, the result is cell 8 Muscle cells have a large number of
death because of waste accumulation. mitochondria because their function is to allow
movement. Mitochondria produce ATP, and ATP
2 Paramecia are heterotrophs and must gain
is essential to enable special proteins to slide
their nutrition by ingestion of nutrients from
alongside one another and create movement. If
their surroundings. Chlorella are autotrophs
ATP is not present, movement is not possible.
and are able to capture sunlight to carry out
photosynthesis, thus they can make their own 9 Mitochondria and chloroplasts, because
nutrition. they have their own DNA; have an additional
outer membrane, indicating a need for
3 These cells have very specific roles in the
greater protection within a potentially hostile
organism. Nerve cells conduct impulses, and
environment; have ribosomes similar to
to do this they require adaptations that allow
prokaryotic ribosomes; divide by simple fission.
depolarization and repolarization or rapid
electrical changes within them. Muscle cells 10 Chloroplasts produce simple carbohydrates.
produce movement; they possess certain These carbohydrates are sources of chemical
proteins and specific arrangements of these energy when their chemical bonds are broken.
proteins to bring about movement. The result The energy can be used to produce ATP, which
is that nerve and muscle cells carry out their is necessary for cellular activities. Mitochondria
functions without expending valuable time and enable the breakdown of the chemical bonds to
energy in a reproductive stage. release the energy.
4 Even though stem cells are capable of great 11 The presence of a scale bar means that the
variation in what they differentiate into, they still actual size of the object in the micrograph can
have nuclear DNA as their controlling factor. The be worked out.
DNA of one animal is potentially quite different
12 The hydrophilic portions of the phospholipids
from the DNA of another.
align themselves to the locations where the polar
5 The DNA is more vulnerable to the life functions molecules of water exist (outside and inside the
of the cell. These cell functions require enzymes plasma membrane). The hydrophobic protions of
and raw materials, and produce products that the phospholipids align themselves to the inside
may potentially damage the DNA. This creates a of the membrane where there is no contact with
greater chance of interactions and mutations or the polar water molecules.
harmful changes.
13 There is no cholesterol in the membranes of
6 Pili are plasma membrane extensions that allow plants and plant products. Animal products have
bacterial cells to join so that exchange of DNA plasma membranes, which contain cholesterol.
1
,Answers
14 Amphipathic phospholipids have both 23 The chromosomes would be abnormally
hydrophilic and hydrophobic properties. distributed, resulting in cells with improper DNA
to govern cellular processes. The result would
15 Molecules of carbohydrates producing
be abnormal cells that probably would die
glycoproteins.
very early.
16 In passive transport, the driving force is the
24 Since the chromatids are yet to separate in
concentration differences of a particular
metaphase, there would be 48 chromatids
substance type. When concentrations are high,
present.
molecular collisions occur more frequently
resulting in movement towards areas of lower 25 Cytokinesis occurs at the conclusion of the M
concentration. This movement outwards will phase (mitosis) and just before interphase begins
continue until collisions are occurring equally (G1).
throughout the area, by which time equilibrium
26 Animal cell cytokinesis involves pinching in
is said to be established. In active transport,
of the plasma membrane from the outside to
there is no final equilibrium. Active transport is
separate the two sets of chromosomes. Plant
movement against a concentration gradient with
cell cytokinesis involves the formation of a cell
the expenditure of energy.
plate that develops between the cell wall and
17 Non-polar amino acids are present because the plasma membrane to separate the two sets of
inner region of the membrane is made of the non- chromosomes; the cell plate forms inside the cell
polar regions of the membrane phospholipids. and builds toward the exterior cell wall.
18 Both exocytosis and endocytosis require 27 The mitotic index can be used to predict the
expenditure of energy in the form of ATP. response of cancer cells to chemotherapy. The
higher the index, the faster the rate of mitosis.
19 Bacteria in the air were able to enter the flask
and grow in the nutrient broth.
20 Diverse explanations are possible here. There
Practice questions
is no clear evidence of how the first nucleus
developed. It may have developed as mitosis-
1 (a) (i) interphase because no (individual)
like divisions resulted in compact genomes. It
chromosomes are visible/
may have occurred with plasma membranes
genetic material visible as chromatin/
breaking into the interior, resulting in the nuclear
chromosomes/DNA has not
membrane. This is presently being hypothesized
condensed/nuclear envelope/
and researched.
nucleolus/nucleus is visible (1)
21 Emergent properties indicate greater outcomes
(ii) DNA synthesis/replication/OWTTE;
for the whole than would be expected when
(cell) growth/increase in the number of
simply adding up the individual abilities of each
organelles/specific organelle mentioned;
part. When Hatena and the alga combine, their
transcription/synthesis of RNA (2 max)
abilities are pooled together, allowing greater
abilities than anticipated. Mark only the first process on each line
if more than two processes are listed.
22 The cells on Earth today are here because of
Do not accept error carried forward if
changes to the first cells that appeared on Earth.
mitosis is the answer in (i).
Endosymbiosis and other changes resulted in
the more complex cells of today compared with (b) retain the capacity to divide; they are
the very simple first cells. undifferentiated/unspecialized;
2
, have the ability to differentiate (along (c) stem cells are undifferentiated cells;
different pathways)/are multipotent/ embryo cells are stem cells; stem cells can
pluripotent/totipotent (2 max) differentiate in many/all ways/are pluripotent/
Mark only the first process on each line if totipotent; differentiation involves expressing
more than two processes are listed. some genes but not others; stem cells
can be used to repair/replace tissues/heal
(c) named source of stem cells e.g. bone
wounds (3 max)
marrow/cord blood/inner cell mass of
embryo/embryonic stem cells; name of (Total 6 marks)
condition that is treated using the stem cells
e.g. leukaemia/heart disease/diabetes/other
possibility; one precise detail of how the Challenge yourself
stem cells replace/replenish (differentiated)
cells that are the cause of the condition 1 ‘Response’ is the function of life demonstrated.
(3 max) This response allows the paramecia to move to
Example: a location where it is most likely to survive.
Source: stem cells obtained from bone
2 Nutrition.
marrow;
Condition: leukaemia; 3 Excretion.
Detail: patient’s bone marrow cells (are killed
4 A contractile vacuole expands as water
and) replaced with the stem cells
concentrations increase in a microorganism.
(Total 8 marks)
Once fully expanded, the contractile vacuole
2 A (Total 1 mark) then contracts, pushing excess fluids through
the attached radiating canals. Non-digestible
3 C (Total 1 mark)
food that enters paramecia exit the cell via the
4 D (Total 1 mark) anal pore.
5 (a) (i) 50 000 (Accept answers in the range of 5 Things to note on the drawing: The plasma
50 000 to 53 000)(1) membrane should be adjacent to but separate
(ii) 0.1 µm (units required) from the cell wall. The ribosomes should be dot-
Allow answers in the range of 0.09 µm like structures within the cytoplasm because
to 0.12 µm(1) of their small size. In the case of ribosomes
there should be many, many dots, reflecting the
(b) Award [1] for any two of the following. large numbers of ribosomes that occur in most
growth/production of (extra) body cells; (do bacterial cells.
not accept cell growth)
first stage of spermato/oo/gametogenesis/ cell wall
forming oogonia/spermatogonia; cell membrane
embryo development; DNA
wound healing/(tissue)
repair/hair growth/
replacement of skin cells;
{ (do not accept
repairing cells)
ribosome
peptidoglycan flagellum
clonal selection/division of lymphocytes (for
antibody production)
Do not accept asexual reproduction. Do not
outer membrane pili
award a mark if one of the
first two answers is incorrect. (1 max)
3
,Answers
6 Diffusion. small
prokaryotic
cell
7 There is no expenditure of energy on the part of
the cell.
8 As solutes move from the blood into the dialysate,
the concentration gradient of the solutes between large
prokaryotic
the blood and the dialysate decreases, which cytoplasm
cell
slows the cleansing process of the blood.
double
9 Characteristics that affect the rate of movement membrane
include the size of solute particles, the charge of
solute particles and the concentrations of solute
15 More than 900. However, the number should
particles on both sides of the membrane.
not be too high as interphase still is the longest
10 Osmosis. phase of the cell cycle with cancer cells.
11 Factors affecting the time needed include the 16 The cancer cells would have a shorter cell cycle
concentration of solutes and wastes in the time, thus illustrating their more rapid growth
blood, the percentage water composition of the rate.
blood (due to adequate or inadequate hydration),
17 The cancer tissue has a higher mitotic index
and the actual types of solutes and wastes
because they are dividing at a more rapid rate.
present in the blood.
12 The cells will gain mass. This is because when
cells are placed in a hypotonic solution, there
are fewer osmotically active particles outside the Labs
cells than inside. That means there is a higher
concentration of water molecules outside the 1.1 Chlorella and the functions of life
cells than inside. Because of osmosis, water will
then move into the cells along a concentration 7 Response and nutrition should be mentioned
gradient. here. Response is the movement towards light
so that photosynthesis can occur. Nutrition is
13 The salt particles are osmotically active the process whereby the organism uses light to
particles in the soil. Because of the larger produce most of the nutrients it needs to survive.
number of particles in the soil, there is a higher The Chlorella would eventually die in the dark
concentration of water in the cells than in the once the supply of nutrients had been used up.
soil. Water leaves the roots, resulting in death of
the plants. Plants will not grow in this area until 1.2 The use of a light microscope to investigate
the salt particles are washed away. cells and cell structures
14 The drawings should follow the most logical 4a 5000
explanation: (1) the bacterial cell (potential 4b 250 µm
organelle) comes into contact with the larger cell;
(2) engulfing (phagocytosis) occurs; (3) a section 4c 10 mm
of the larger cell’s plasma membrane surrounds 1.4 Membrane transport
the engulfed bacterial cell; (4) two membranes
are now present, the one provided by the 9 The point at which the line of the experimental
receiving cell and the one already intact on the results crosses the x-axis indicating zero per
bacterium. cent change should indicate the osmolarity of the
4
,potato tissue. The actual value will vary because of Answers regarding how the procedure could be
variations in potatoes and procedural variations. altered will vary depending on the exact details
of the procedure carried out by the student.
For the data points on the graphs to be
Suggestions should include meaningful and not
accurate, measurements must be extremely
elementary explanations.
accurate. Even slight errors in procedures and/
or measurements will result in data that will not
yield valid conclusions.
5
, Answers
Chapter 2 Answers are not provided for questions that require individual research or practice.
Exercises
1 (a) H Chemical reactions are only possible in cells,
blood plasma, etc., because the majority of
H C OH solutes in living organisms are polar and are thus
water soluble. Polarity is also directly related
H
to cohesion and adhesion of water molecules,
Formula = CH4O and is important in any answer dealing with
formula = CH4O
or CH
orCH 3OH
3
OH movement of water. Maintenance of a stable
internal temperature is directly related to the high
(b) H H O specific heat of water, and also attributed to the
polarity of water molecules.
H N C C OH
6 glycerol + 3 fatty acids → triglyceride + 3 water
H
7 trans fatty acid, saturated fatty acid, unsaturated
Formulaformula
= C2H=5O
C22HN5O2N fatty acid.
8 Body mass does not account for differences in
2 (a) Many glucose molecules.
heights between individuals.
(b) Lactose and water.
9 (a) Proline.
(c) One glycerol and three fatty acid molecules.
(b) Methionine and cysteine.
3 Metabolism is a combination of anabolism
(c) Aspartic acid, glutamic acid, lysine, arginine,
and catabolism. Anabolism often involves
and histidine.
small ‘building block’ molecules being bonded
together by condensation reactions into 10 75 (there is always one less peptide bond than
macromolecules. Catabolism often involves the the number of amino acids).
hydrolysis of macromolecules into monomers.
11 160 000 combinations. Each position would
4 Many different possible answers exist for this have a 1 in 20 chance of being any one amino
question. You should pick an organism that acid. Thus, 20 × 20 × 20 × 20 = 160 000.
you are familiar with. Ways in which water is
12 The specificity is explained by a combination
important could include, but are not limited
of molecular shapes that must correspond and
to: water for cytoplasm in every cell; blood
molecular charges that must align. The substrate
plasma; environment for all chemical reactions;
must have a complementary/opposite shape to
distribution of nutrients within the organism;
the active site of the enzyme. In general, if an
distribution of wastes within the organism;
enzyme has an internal positive charge, then the
habitat for some organisms; redistribution
substrate will have a negative charge, although
of water often changes the shape of some
there are exceptions to this.
cells/organisms (e.g. guard cells in plants);
maintenance of stable internal temperature. 13 They are neither a reactant nor a product. In
addition, they influence the rate of the reaction.
5 Answers for this question are also expected
The difference between a non-enzyme catalyst
to be highly varied. Many answers will and
and an enzyme is that an enzyme is organic.
should focus on the polarity of water molecules.
1
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