Outline the control of the heartbeat. [6]
• Pacemaker controls heartbeat. Pacemaker is located in the right atrium. It stimulates atria to contract.
Ventricles subsequently contract after atrial contraction. Nerves can stimulate the heartbeat.
Neurotransmitters such as noradrenaline can speed up heartbeat. Neurotransmitters such as
acetylcholine can slow down the heartbeat. Hormones can also stimulate the heart rate. Adrenaline from
the adrenal glads can cause increased heart rate.
State four molecules transported by the blood. [4]
• Oxygen is used for aerobic respiration.
• Carbon dioxide is waste material from aerobic respiration.
• Glucose is needed for aerobic respiration.
• Hormones is needed for transmission of messages.
• Antibodies is to fight for infection.
• Urea is a waste product.
Outline the process of inspiration in humans. [4]
• During inspiration, diaphragm and external intercostal muscles contract, which raises the rib cage
upward. This increase the volume of lungs, which in turn causes decrease in the pressure level inside
the lungs, as compared to outer atmospheric pressure. Hence, air enters the lungs, due to higher
pressure outside the body. Air flows to the lungs through trachea and bronchi.
Describe the functions of valves in the mammalian heart. [4]
• Valves present in the heart prevents the back flow of blood. Opening and closing of these valves control
the duration of cardiac cycle. Closing of semilunar valves, allows ventricles to fill up, which in turn
increases the pressure in the ventricles. Valves open when the pressure rises. Bicuspid and tricuspid
valves prevent the back flow of blood from ventricles to atria. Similarly, semilunar valves prevent back
flow of blood from arteries to ventricles.
Explain how blood solute concentrations are kept within narrow limits in the human body. [7]
• The concentration of solute in the blood is monitored by the hypothalamus. When the concentration of
solute is higher in the blood, pituitary gland releases Anti-diuretic hormone (ADH), which increases the
permeability of the colllecting duct to water. More aquaporins released in the plasma membrane of the
collecting ducts and hence more occurs very easily. This causes passage of concentrated urine. In
opposite case, if the solute concentration is low, less amount of ADH will be secreted, causing less
permeability of the collecting duct to water. This will lead to very less reabsorption of water and hence,
passage of dilute urine. Insulin reduces the blood glucose level. Excess glucose is stored in the liver in
the form of glycogen. Glucagon increases the blood glucose level. This is due to negative feedback.
Outline the functions of rough endoplasmic reticulum and Golgi apparatus. [3]
Draw a labelled diagram of a eukaryotic plant cell as seen in an electron micrograph. [4]
Outline how the energy flow through food chains limits their length. [3]
• a. light energy of Sun is converted by plant/autotroph to chemical energy «in carbon compounds
through photosynthesis»
• b. detritivores/saprotrophs decay plant material «that accumulates in the soil» to obtain energy
OWTTE
• c. consumers release energy from the carbon compounds by cell respiration energy lost as heat
• d. energy is used by organisms for metabolism
• e. energy is transferred between organisms/trophic levels through the food chains/web
For mp e, accept specific example such as energy is transferred from primary to secondary consumer
etc.
• f. energy is lost at each trophic level «so lengths of food chains/web are restricted»
OR
approximately 80/90 % of energy is lost «between trophic levels»
• Only a small proportion 10-20% of energy can pass from one trophic level to the next and a large
proportion 80-90% lost between one trophic level and the next.
• Energy released from carbon compounds by respiration is used in living organisms and converted to
heat. Energy released by respiration AND lost as heat.
• Energy can also be lost due to feces and uneaten parts of food. There would be more energy if feeding
was at an earlier stage in the food chain.
In hot, dry conditions plants lose water rapidly due to transpiration. Explain how the structures and
processes of the plant allow this water to be replaced. [8]
• A
Explain how reduction division results in genetic variety [8]
• Reduction division occurs during meiosis. Sets of replicated homologous chromosomes pair up in the
equator. Each chromosome in homologous pair came from maternal or paternal parent.
• Maternal and paternal chromosome in each pair is randomly oriented to either side of cell.
• Homologous chromosomes separate, and each moves to opposite pole. Cell undergoes meiosis I.
• Sets of replicated chromosomes separate again. Two cells from first division undergo meiosis II.
• One cell has given rise to four cells. Diploid number 2n becomes haploid number n. Haploid cell
contains only one chromosome from each original homologous pair. Different haploid cells form
because of independent assortment during meiosis is basis for first variety. Mixture of maternal and
paternal chromosomes in any haploid cell is different.
Explain the relationship between polypeptides and genes [8]
• DNA codes for a specific sequence of amino acids. The DNA code for one polypeptide is a gene. DNA
is transcribed into mRNA. mRNA moves to a ribosome, where mRNA is translated into a polypeptide.
mRNA, tRNA and ribosomes are essential for translation. Translation links amino aids, to make
polypeptide. Originally, it was thought that one gene always codes for one polypeptide. Some genes do
not code for a polypeptide. Some genes code for transfer RNA.
• However, some sections of DNA code for regulators that are not polypeptide. Change in the gene
(mutation) will affect the primary structure of the polypeptide. Universality of genetic code means all
organisms show same relationship between polypeptides and genes. This provides evidence for
common ancestry.
Describe the genetic code and its relationship to polypeptides and proteins. [5]
• The genetic code is based on sets of three nucleotides called codons. Bases include adenine, guanine,
cytosine and thymine in DNA. Each codon is code for one amino acid. Some codons are start or stop
codons. DNA is transcribed into mRNA by complementary base pairing. mRNA is translated into a
sequence of amino acids. Each gene codes for polypeptide. Polypeptide may be joined to form proteins.
Meiosis in humans produces cells that participate in fertilization. Outline the processes involved in
meiosis. [5]
• Meiosis reduces a diploid cell into four haploid cells. During prophase I homologous chromosomes pair
up. Crossing over occurs at this stage. In metaphase I, homologous chromosomes line up at the equation
of the spindle. In anaphase I, homologous chromosomes separate and move to opposite poles. In
telophase I, chromosomes reach poles and unwind. In prophase I, chromosomes condense and become
visible, new spindles are formed. In metaphase II, chromosomes line up at the equator. In anaphase II,
sister chromatids separate. In telophase Il, chromatids reach the poles and unwind.
Explain how males inherit hemophilia and how females can become carriers for the condition. [8]
• Hemophilia is due to a recessive allele. It is a sex-linked disease. Sex-linked conditions tend to be more
commonly expressed in males. Sex chromosomes in female are XX while males are XY. Xh is allele for
hemophilia and XH is allele for normal. Male has one X and one Y chromosome, therefore has only one
copy of gene located on X chromosome. X chromosome in males comes from female parent. Any male
receiving allele from mother will express the trait. Males have only one copy so recessive trait is not
masked. Hence, XhX is genotype for hemophilia. Males have a 50% chance of hemophilia is mother is
a carrier. Heterozygous XHXh female is a carrier. Female inherit one X chromosome from father and
one from mother. Hemophiliac males have carrier daughters. Hemophilia allele could have been
inherited from either parent.
Describe the properties of water that make it a useful component of blood. [4]
• Water is a polar molecule. This makes it a good solvent. Water is liquid at body temperature. Nutrients,
metabolic wastes, hormones and blood cells are transported by water. Also, high heat capacity allows
water to carry heat without warming up. This allows blood to move heat for warning.
Explain how antibodies are produced in response to infection in humans [8]
• Pathogens are foreign substances that cause diseases. It has antigens on their surface which stimulate
antibody production. Many types of B lymphocytes exist in the body, and each recognizes one specific
antigen. Antigen binds to proteins in plasma membrane of specific lymphocyte, and this recognition of
antigen activates lymphocyte. Activated lymphocyte divides many times and clones itself through
mitosis to produce many identical lymphocytes. Lymphocytes produce the specific antibody against
antigen that are proteins synthesized through translation, by ribosomes.
• Antigens are foreign substances/pathogens. Antigens stimulate antibody production. organisms causing
disease have antigens (on their surface); antigen is recognized by antibody of (one type of) lymphocyte;
humans have many types of lymphocytes of which one type can recognize a particular antigen;
recognition of antigen activates lymphocytes; activated lymphocyte divides many times; clone of
lymphocytes results; lymphocytes produce/secrete antibodies; antibodies are proteins; proteins are
synthesized by ribosomes / by the rough endoplasmic reticulum;
Describe the production of antibodies. [6]
• Antibodies are produced by (B) lymphocytes; many types of lymphocytes exist in the body; each
recognizes one specific/OWTTE antigen (from foreign body); antigen binds to (proteins in plasma
membrane of) specific lymphocyte; activates the lymphocyte; (lymphocytes) clone (through mitosis); to
produce many identical lymphocytes; which secrete the specific/OWTTE antibody against the antigen;
that are proteins made through translation/protein synthesis;#
Outline the mechanisms of defense against pathogens in humans. [7]
• Leukocyte-white blood cell
• Phagocytic leukocyte is a white blood cell that ingests pathogens through phagocytosis
• Macrophage is a type of phagocytic leukocyte
• Lymphocytes are T, B cells- They are not involved in physically attacking the pathogens in the same
way, they are rather involved in antibody production
• Skin membranes acting as a barrier to pathogen is the first lines of defense. Sebaceous glands secrete
lactic acid and makes surface of skin acidic. Skin acid prevents growth of many pathogens. Lysozyme
in mucus can kill bacteria. Pathogens caught in sticky mucus and removed from body. Inflammatory
response can cause swelling or redness to inhibit the pathogen. Phagocytic leukocytes are present in the
blood. They leave capillaries and go into body tissues. They concentrate at sites of infection, and
attracted to pathogens. They ingest pathogens in blood. Phagocytosis occurs by endocytosis.
Macrophages present antigens. Therefore in response to antibodies, they kill and digest pathogen
(phagocytosis) by endocytosis using lysosomes. Plasma membrane forms around pathogen to form a
vacuole, and lysosomes digest the contents of vacuoles. Specific lymphocytes recognize one specific
antigen. Antigen-specific lymphocytes clone themselves, and then produce antibodies. Therefore,
number of antibodies increases.
Discuss the causes, transmission and social implications of AIDS. [8]
• Cause: AIDS is caused by HIV. HIV reduces the effectiveness of the immune system by reduction in the
number of active lymphocytes. This leads to the loss of the ability to produce antibodies, results in
lower immunity. The infected person is susceptible to other infectious diseases. AIDS is the observed
syndrome when final stage of infection develops.
• HIV transmission: Fluids from an infected person transmit HIV. Blood transmissions Blood