contents · all the core topics required for sl and hl are ... answers and markschemes can be...
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Chapter 1 Cell biology
1.1 Introduction to cells 2
1.2 Ultrastructure of cells 7
1.3 Membrane structure 11
1.4 Membrane transport 14
1.5 The origin of cells 19
1.6 Cell division 21
Chapter 2 Molecular biology
2.1 Molecules to metabolism 34
2.2 Water 36
2.3 Carbohydrates and lipids 39
2.4 Proteins 49
2.5 Enzymes 51
2.6 Structure of DNA and RNA 55
2.7 DNA replication, transcription and translation 57
2.8 Cell respiration 62
2.9 Photosynthesis 64
Chapter 3 Genetics
3.1 Genes 76
3.2 Chromosomes 79
3.3 Meiosis 84
3.4 Inheritance 90
3.5 Genetic modification and biotechnology 96
Chapter 4 Ecology
4.1 Species, communities and ecosystems 108
4.2 Energy flow 113
4.3 Carbon cycling 115
4.4 Climate change 120
ContentsAll the core topics required for SL and HL are covered in Chapters 1 – 6. Additional HL topics are covered in Chapters 7 – 11.
Chapter 5 Evolution and biodiversity
5.1 Evidence for evolution 130
5.2 Natural selection 133
5.3 Classification of biodiversity 135
5.4 Cladistics 144
Chapter 6 Human physiology
6.1 Digestion and absorption 154
6.2 The blood system 158
6.3 Defence against infectious disease 166
6.4 Gas exchange 169
6.5 Neurons and synapses 173
6.6 Hormones, homeostasis and reproduction 178
Chapter 7 Nucleic acids
7.1 DNA structure and replication 192
7.2 Transcription and gene expression 198
7.3 Translation 202
Chapter 8 Metabolism, cell respiration and photosynthesis
8.1 Metabolism 214
8.2 Cell respiration 219
8.3 Photosynthesis 224
Chapter 9 Plant biology
9.1 Transport in the xylem of plants 236
9.2 Transport in the phloem of plants 243
9.3 Growth in plants 247
9.4 Reproduction in plants 250
Chapter 10 Genetics and evolution
10.1 Meiosis 260
10.2 Inheritance 262
10.3 Gene pools and speciation 270
Chapter 11 Animal physiology
11.1 Antibody production and vaccination 282
11.2 Movement 286
11.3 The kidney and osmoregulation 292
11.4 Sexual reproduction 299
Index 311
Practice Test 1 (Standard Level) Paper 1 & 2
Practice Test 2 (Higher Level) Paper 1 & 2
Answers and markschemes can be downloaded for free at www.ntk.edu.hk.
1.1 Introduction to cells
1.1.1 Cell theoryThe cell theory explains the relationship between cells and living organisms. The three
statements of the cell theory are:
1. All living organisms are composed of cells.
Whether unicellular or multicellular, all living organisms are made up of cells. This
can be confirmed using a microscope.
2. Cells come from pre-existing cells. (Refer to Topic 1.5)
3. The cell is the smallest unit of living organisms.
Organisms made up of only one cell (unicellular) can carry out all the functions of life:
• Nutrition — Cells either produce their own organic nutrients (autotrophic nutrition) or acquire organic nutrients from other living organisms
(heterotrophic nutrition). Chlorella (Figure 1.1.1) and Scenedesmus (Figure 1.1.2)
are autotrophic unicells, which can produce their own organic nutrients.
Escherichia coli (E. coli) (Figure 1.1.3) is an example of a heterotrophic unicell.
Figure 1.1.1 Chlorella contain green pigments for photosynthesis.
Figure 1.1.3 Escherichia coli can cause diseases, but is useful in biotechnology.
Figure 1.1.2 Scenedesmus, another photosynthetic organism.
• Metabolism — Cells perform life-sustaining chemical reactions such as
protein synthesis to produce the building blocks of life. Cells also generate energy,
in the form of ATP in a process called cell respiration (refer to Topic 2.8).
• Growth — Cells increase in size over a period of time. When a cell reaches a
certain size, it can no longer grow, and has to split to form new cells.
• Response — Cells are able to respond to changes in their internal and external
environments, for example, a change in temperature or pH levels. Responses are
important for cells to adapt to a changing environment.
Cell biology1C h a p t e r
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• Excretion — Waste materials are produced during metabolic reactions. For
example, carbon dioxide is formed in cell respiration. Removing metabolic wastes
from cells is important to prevent accumulation of toxic substances which may
disrupt normal cell activities.
• Homeostasis — Living in a stable environment is important for a cell. For
example, cells living in a freshwater environment should be able to remove excess
water, or else excess water uptake may cause the cell to burst.
• Reproduction — Producing offspring is one of the major features of living cells.
Experiments show that cells cannot be produced from a lifeless environment. It is
reasonable to conclude that all cells have come from pre-existing cells.
Unicellular organisms, such as Paramecium (Figure 1.1.4), show how cell structures can
perform the functions associated with life:
Contractilevacuole
Nucleus
Food vacuole
Plasma membrane
Cilia
Cytoplasm
• Food vacuoles contain nutrients engulfed from the surroundings.
• The nucleus contains genetic information which controls cell activities. The genetic
information will also be passed to offspring after cell division.
• A contractile vacuole pumps excess water out of the cell when the organism is
living in a freshwater environment.
• Cytoplasm contains enzymes to carry out metabolic reactions.
• The plasma membrane is partially permeable. It controls movement of substances
into and out of the cell and helps the cell excrete metabolic wastes.
A cell contains sub-cellular structures which are enclosed by a plasma membrane. They
help the cell to maintain a specific set of conditions to perform specific reactions inside
the cell. A cell also contains genetic information for its functions. However, there are
situations in which cells may show differences from the generic structures shown
above:
• Striated muscle fibres — Striated muscle fibres (Figure 1.1.5) are cells that are
responsible for movement in humans. They are different from other cells in that
they have more than one nucleus in the cytoplasm.
• Aseptate fungal hyphae — Fungal hyphae are thread-like structures composed
of fungal cells. However, the fungal cells in aseptate fungal hyphae (Figure 1.1.6)
merge to share sub-cellular contents such as the cytoplasm and nuclei. Cells are
not divided by the plasma membrane or the cell wall in the hypha.
COMMON MISTAKEBe careful not to mix up the terms excretion and egestion.• Excretion: the removal of
metabolic wastes (like urea and carbon dioxide) and excess substances from the body (through breathing, sweating and urination).
• Egestion: the removal of undigested substances from the body through the anus.
Figure 1.1.4 Paramecium
Figure 1.1.5 Striated muscle fibres in skeletal muscles contain multiple nuclei.
Nuclei
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Chapter 1 Cell biology
Cell wall
Plasma membrane
Cytoplasm
Ribosome Nucleus
Figure 1.1.6 An aseptate fungal hypha
• Giant algae — As the name suggests, the size of these organisms is greater than
that of normal cells, which measure around 100 μm to 1 mm long on average.
Giant algae can grow to a size as large as 100 mm.
1.1.2 Use of microscopeThe microscope is an essential equipment for investigating cell structures and functions.
Figure 1.1.7 Red blood cells and white blood cells
The above light micrograph shows red blood cells and white blood cells. Using the
provided scale bar, the magnification can be calculated.
Magnification = Image size
Object size
The image size and the object size have to be in the same unit.
The micrometer (μm) is a common unit used in cell biology. It is 1 000 times smaller
(10−3) than a millimeter (mm) and 1 000 times larger (103) than a nanometer (nm).
1.1.3 The importance of the surface area to volume ratioCells obtain nutrients (e.g. glucose) from their surroundings and release waste
materials (e.g. carbon dioxide) to the surroundings. The movement of substances into
and out of cells mainly relies on diffusion. Therefore, the rate of diffusion is crucial
for cells because it directly affects the amount of nutrients that the cell can obtain for
growth.
When cell size increases, the cell needs extra nutrients to sustain life, and it also
produces more waste which has to be excreted to the surroundings. So the cell size has
to be optimal in order to obtain enough nutrients and remove excess substances.
The surface area to volume ratio of a cell is one of the factors that determine how
fast substances can diffuse into and out of the cell, and this ratio is affected by the size
of the cell. Figure 1.1.8 illustrates how the size of an object affects the ratio.
EXAM TIPAs mentioned, the scale bar can be used to calculate the magnification. All measurements should be in the same unit. Using Figure 1.1.7 as an example:• The measured length of the
scale bar is 5 mm (5 × 10−3 m).
• The indicated length of the scale bar is 10 μm (10 × 10−6 m).
• Magnification
= 5 × 10−3
10 × 10−6 = 500 ×
Therefore the magnification of Figure 1.1.7 is 500 × .
10 μm
White blood cellRed blood cell
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When cell size increases, the surface area to volume ratio decreases. This reduces the
diffusion rate, and the cell cannot obtain enough nutrients or excrete excess waste
materials.
2 cm
4 cm
6 cm
8 cm
Surface area (cm2) 24 96 216 384
Volume (cm3) 8 64 216 512
Surface area to volume ratio 3 : 1 1.5 : 1 1 : 1 0.75 : 1
Figure 1.1.8 The size of an object (e.g. a cube) determines the surface area to volume ratio.
Cells have their optimum sizes, which allow materials to be exchanged efficiently.
When a cell reaches a certain size, it will either stop growing or split into two cells in
order to maintain the optimum size. For example, the size of a bacterium is normally
around 1 μm.
Multicellular organisms like humans are too large to simply rely on diffusion to obtain
nutrients from their surroundings. Therefore, humans have specialized organs to
absorb nutrients to support life. Humans also have specialized organs to excrete waste
materials. This shows the emergent property of multicellular organisms, i.e. the
performance of the whole organism is greater than the sum of the performance of
individual cells.
1.1.4 Stem cells and cell differentiationStem cells are undifferentiated cells that have the capacity to divide indefinitely, and
they do not have specialized functions. The daughter cells formed from stem cells can
differentiate into specialized cells which perform specific functions, and this is done by
expressing some genes but inactivating other genes in the cell.
Cell differentiation is important in forming multicellular organisms because this
helps the organism to form different types of cells to perform specific functions, for
example red blood cells to transport oxygen and lymphocytes to produce antibodies.
The ability of cells to divide and differentiate is known as cell potency. Using the
concept of potency, stem cells can be classified into three types:
Totipotent cell Pluripotent cell Multipotent cell
SourceZygote or cells in the first two divisions of mitosis
Embryonic stem cells Adult stem cells
Cell potency
Can form any tissue, including embryonic and placental tissue
Can form any tissue except embryonic and placental tissue
Can only form specific types of cells
Table 1.1.1 Classification of cells based on cell potency
The potency of stem cells is important in embryonic development and in determining
the use of stem cells for therapeutic purposes.
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Chapter 1 Cell biology
1.1.5 Stem cell therapyStem cell therapy is the use of stem cells to regenerate healthy tissues or organs to
replace damaged ones. It can be used to cure diseases such as:
• Stargardt’s disease — an inherited disease that causes macular degeneration
(deterioration of the central region of the retina). Stem cell-based therapies are
being developed with the hope of curing this disease. By injecting embryonic stem
cells into the eye, the stem cells will then be differentiated into photoreceptor cells
in the eye. Trials have been done on mice as well as humans.
• Leukemia — a cancer of white blood cells, or leucocytes. Although chemotherapy
has been used to treat this disease, abnormal leucocytes cannot be completely
eliminated by this method. Bone marrow transplantation is an alternative method
to chemotherapy. Before transplanting healthy bone marrow stem cells into the
patient, the original bone marrow and the abnormal leucocytes have to be killed
first. This can be done by chemotherapy. Then the healthy bone marrow stem cells
can be introduced and can start producing new healthy leucocytes to replace the
abnormal cells.
There is an ethical dilemma in stem cell research which arises from the fact that embryonic stem cells have the
greatest potential for differentiating into almost any type of tissue, which can be manipulated in therapeutic
cloning. But with current technology, embryonic stem cells can only be obtained by destroying early-stage embryos.
Therapeutic cloning can help patients who are in need of organ transplants. Organs created this way will not
initiate immunological rejection and patients no longer have to rely on organ donors. Therapeutic cloning
involves the fusion of an enucleated egg (egg cell with the nucleus removed) with a somatic nucleus (nucleus
from a body cell) and the extraction of the inner cell mass of the embryo.
NATURE OF SCIENCEOn one hand, stem cell research is gaining in importance and has great curative potential, but on the other hand, ethical issues concerning laboratory protocols are raised.
Somatic-cell nuclear
transfer
EmbryoZygote
Egg cell
Skin cell
Removenucleus
Fusion
BlastocystExtract
inner massCultured pluripotent
stem cells
Figure 1.1.9 Therapeutic cloning of stem cells
Opposing viewpoints on stem cell research and therapeutic cloning include:
For• An early stage embryo is just a ball of cells that have not developed the essential features of a human being.
• Not until day 14 will the nervous system of embryos start to develop. Embryos do not experience pain or
other sensations.
• Large numbers of excess embryos produced in in vitro fertilization (IVF) are not given the chance to live. It is
better to use the stem cells for research to save lives rather than to discard the embryos.
Against• Embryos have the potential to develop into human beings. They should not be deprived of the chance to live.
• The embryo should be protected from the time of fertilization and treated as a human being.
It is still controversial whether human beings have the right to destroy embryos and use them in developing a
technique for therapeutic cloning.
AIM Ethical issues of stem cell research and therapeutic cloning
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