AHS 2021 Flashcards
Explain how dialysis works to remove metabolic wastes, while preventing useful substances from leaving the blood. [4] (AHS 2021)
- Blood flows through a partially permeable dialysis tubing bathed in dialysis fluid;
- The dialysis fluid contains no urea, to ensure that urea will diffuse out of the blood into the fluid;
- Fluid contains useful substances like glucose/ amino acids/ salts at concentrations similar to those of a healthy person, to prevent these from diffusing out of the blood;
- While excess salts and water move out by diffusion and osmosis respectively;
- Molecules like proteins, platelets and blood cells (any two) are too large to diffuse through the dialysis tubing;
(any 4, but must address both parts of the qtn)
State one structural feature of the vein, and explain how the feature is related to the vessel’s function of returning blood to the heart. [2] (AHS 2021)
Has valves;
To prevent backflow such that blood flows in one direction back to the heart;
OR
Has a large lumen relative to the diameter of the entire vessel;
To reduce resistance to blood flow;
OR
Less elastic/muscular walls (than arteries);
Enables vein to be squeezed by (surrounding skeletal) muscles to push the blood along
Explain the series of events that occurred to bring about the change in blood glucose concentration from between the hepatic portal vein and the artery. [3] (AHS 2021)
- Blood glucose conc. above the norm stimulated the islets of Langerhans in the pancreas;
- Which released more insulin into the bloodstream;
- Stimulating the conversion of excess in the blood glucose into glycogen in the liver, reducing glucose levels
Describe how a carbon dioxide molecule from the air reaches a chloroplast in a mesophyll cell in the leaf. [4] (AHS 2021)
- Carbon dioxide diffuses through the stomata;
- into the intercellular air spaces;
- Dissolves in the thin film of moisture on the (spongy/palisade) mesophyll cells;
- Diffuses into chloroplast of mesophyll cell;
The rate of uptake of carbon dioxide for a plant reached a maximum. Suggest a limiting factor that could have caused this. (sunlight continued too increase) [1] (AHS 2021)
Carbon dioxide concentration/ temperature/ concentration of chlorophyll within the plant
Explain why it is important for the growing plant that the net carbon dioxide uptake during one day is greater than the carbon dioxide released. [2] (AHS 2021)
- So that the glucose produced by the plant is not all used up in respiration;
- This ensures that there is surplus glucose/ food to be used to build new
protoplasm/ some specific fate of glucose contributing to increase in mass described
A shoot was used to set up an experiment, connected to capillary tube with an air bubble. Briefly explain what caused the air bubble to rise up the capillary tube. [4] (AHS 2021)
- Water constantly evaporates from the mesophyll cells in the leaf into the intercellular air spaces;
- before diffusing out of the leaf as water vapour;
- The decrease in water potential in the mesophyll cells causes water to be drawn out of the xylem by osmosis;
- Creating a suction force that pulls water up as a continuous column
A bee transferred pollen from flower S to flower T on the plant. With reference to these two flowers, describe how pollination could have been brought about by the bee on this plant. [3] (AHS 2021)
- Bee lands on the petal on flower S and moves in to collect nectar;
- in the process, pollen on anthers are brushed onto hairy back of insect;
- as bee moves into flower T, its back brushes against the sticky stigma, causing pollen from flower S to be transferred to flower T
first point described at least once, for either flower;
Some people suffer from lactate dehydrogenase deficiency, an inherited disease caused by a mutation to the LDHA gene. The allele responsible for the disease is recessive. People with lactate dehydrogenase deficiency experience fatigue, muscle pain and cramps during exercise.
Using information from the above description as an example, distinguish between the terms “genotype” and “phenotype”. [2] (AHS 2021)
- Genotype refers to the genetic makeup of the organism while phenotype refers to the observable trait;
- An individual with two copies of the recessive allele is homozygous recessive with respect to the LDHA gene (genotype). The individual will exhibit fatigue, muscle pain and cramps during exercise (phenotype)
Explain how a foetus is nourished and protected during its course of development in the uterus. [5] (AHS 2021)
- At the placenta, nutrients and oxygen diffuse from mother’s blood to foetus’ blood (at least two useful substances mentioned);
- Nutrients used for growth;
- Oxygen to enable aerobic respiration in foetus to release energy for growth;
- Antibodies are also transported across the placenta to protect foetus against diseases;
- metabolic wastes diffuse across placenta from foetus’ blood to mother’s blood to be excreted,preventing the build-up of toxic waste products in the foetus;
- The umbilical cord transports blood containing dissolved substances from the fetus to the mother and bice versa;
- Amniotic fluid is incompressible and therefore helps to protect foetus against physical injury/ acts as a shock absorber
- Placenta produces progesterone to maintain the uterine lining to ensure foetus remains connected to mother to continue to receive nutrients for growth
(Any five)
A pregnancy is regulated by the hormonal system, while response to touching a hot object is regulated by the nervous system.
A hormonal response would not be as effective as a nervous response when the body touches a hot object. Use your knowledge of hormonal and nervous responses to suggest why. [2] (AHS 2021)
- Transmission of hormones in the blood is slower than the transmission of nerve impulses through neurones;
- hence nervous control allows a faster/immediate response to the source of danger/ provides effective protection
Describe the effects of excessive consumption of alcohol on the nervous system. [3] (AHS 2021)
- It is a depressant which slows down brain functions, resulting in:
(any 2) - Slower reaction time/ increases reaction time;
- Poor muscle coordination/ slurred speech/ blurred vision;
- May lead to reduced self-control;
Describe the roles of the trachea, thin film of moisture, alveolar wall and red blood cell, from the moment air enters A until the time oxygen leaves the lungs in the blood. In your answer, you should clearly identify
each of the labelled structures. [5] (AHS 2021)
- Gland cells in the trachea (A) produce mucus to trap dust and bacteria particles;
- Cilia on the epithelial cells then sweep the mucus with trapped particles upwards away from the lungs;
-
C-shaped cartilage keep the trachea open by providing structural support, to allow air to pass through;
(MAX 2 for trachea) - Thin film of moisture (B) dissolves the oxygen gas so that it can diffuse into the blood plasma;
- Wall of alveolus (C) is one-cell thick, to shorten the diffusion distance for oxygen to travel to the blood capillary;
- Red blood cell (D) contains haemoglobin to bind to the oxygen to transport it to body cells.
The respiratory system helps to support respiration in the human body.
Explain how “gaseous exchange” is different from “aerobic respiration”. [2] (AHS 2021)
Gaseous exchange occurs between the alveoli and blood capillaries. It is a physical process whereby oxygen diffuses from the alveolus into the blood capillaries, while carbon dioxide diffuses in the opposite direction
Aerobic respiration occurs in the
mitochondria of body cells. It is a chemical process whereby glucose is
oxidised in the presence of oxygen to release energy, and carbon dioxide and water are produced
Location - 1m, Process -1m
Insulin is an example of a protein transported in the blood.
Describe how DNA controls the production of insulin. [3] (AHS 2021)
- Gene for insulin;
- Contains a specific sequence of nucleotides;
- To code for a specific sequence of amino acids to be joined together to form a polypeptide, which coils to form insulin
