Past Exam Papers Flashcards by Grace Illingworth

Which of the options A-D, correctly describes how an endotherm would respond to an increase in temperature? [ 1 mark]

A- dilation of arterioles near the surface of the skin

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Which of the options, A to D, occurs in the nucleus of a cell? [1 mark]

B - synthesis of RNA

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Patients with kidney failure can be treated in different ways.

Which of the following statements describes a feature of peritoneal dialysis? [1 mark]

D - only 1 (urea and mineral ions pass into tissue fluid)

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Which of the statements, A to D, correctly describes the way oxygen is transferred into the blood at the gills? [1 mark]

B - blood and water flow in a countercurrent system with a constant concentration gradient between them

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Which of the following properties of the hormone hCG allows it to be detected in the urine? [1 mark]

B - hCG has a polar mass of less than 69,000

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Which of the following statements explains how ecdysone is able to act on cells near the surface of the body? [1 mark]

C- only 2 (it’s soluble in haemolymph because it is a polar molecule) and 3 (it’s complementary to cell surface receptors on cells throughout the body of some invertebrates

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Which of the statements, A to D, correctly describes the process of adhesion? [1 mark]

A - attraction of water molecules to impermeable walls of xylem tissue

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Explain why moths and bumblebees are described as endothermic. [1 mark]

Scales and hair help to reduce heat loss to the environment

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It is more difficult for moths and bumblebees to maintain their body temperature than for mammals and birds to maintain theirs.

Explain why. [2 marks]

They have a larger SA:Vol ratio and so experience a greater heat loss

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Outline the reasons why insects and other animals need well-developed transport systems. [3 marks]

-high metabolic demand
-requires a lot of oxygen and other molecules to be transported around the body quickly and efficiently
-so a specialised transport is needed to cope with the small surface area to volume ratio

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Suggest two further guidelines for the student to follow to ensure they present their diagrams clearly and accurately. [2 marks]

1- don’t shade structures drawn, even if they appear darker
2- don’t sketch - use clear, continuous lines

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Suggest why blood and faeces have the highest concentration of C-reactive protein and copeptin. [2 marks]

-blood has a high concentration as the liver has a good blood supply
-the faeces have a high concentration as the liver secretes waste products into the bile

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Explain what is meant by a limiting factor. [2 marks]

A factor that will determine the rate of a reaction when at lower levels

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Soluble mineral ions are present in soil.

Explain why water molecules can form hydrogen bonds with nitrate ions. [2 marks]

-attraction between the positively charged hydrogen of a water molecule and the lone pair of electrons on the nitrogen
-allowing a hydrogen bond to form between the 2 atoms

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Fig. 18 shows a process that occurs in the cell surface membrane of the endodermis in the root.

Explain how the events shown cause water to enter the endodermis. [2 marks]

-solutes enter against the concentration gradient by active transport
-reduces the water potential of the cell

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Explain why a plant leaf is described as an organ. [4 marks]

-an organ is made up of several tissues to carry out a specific function
-for example, epidermis, spongy mesophyll
-a leaf is composed of many sub-cellular organelles which each have their own role to help carry out the overall reaction and function of photosynthesis

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Anaerobic respiration in yeast cells requires enzymes.
Which organelle is responsible for synthesising these enzymes? [1 mark]

Ribosomes

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Using this information and your own knowledge, compare the processes occurring in the PCT and DCT. [3 marks]

-both the PCT and DCT use active transport for the movement of ions
-both are involved in selectively reabsorbing essential substances
-the DCT only transports ions but the PCT transports ions and other substances

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State and explain one symptom you would expect to observe as a result of nephrogenic diabetes insipidus. [2 marks]

-lots of urination (more than the ‘normal’ volume of urine produced)
-due to fewer aquaporins in the membrane

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Explain why podocytes are usually unable to undergo mitosis. [3 marks]

-they have already specialised
-so are in G0
-cytoskeleton cannot function

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What features of adult stem cells make them suitable for regeneration of tissues in the kidney? [2 marks]

-multipotent
-can become any type of cell in the kidney

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Membranes are found within and surrounding cells.

Which of the statements, A to D, is not a role of membranes in cells? [1 mark]

C - providing support for the cell

Which of the statements, A to D, best defines species evenness? [1 mark]

B - the relative abundance of each species in an area

Suggest why it was not appropriate to estimate the number of jaguars using the capture-recapture technique. [2 marks]

the estimated number of jaguars in the area will be inaccurate
it’s dangerous for the jaguars

Other evidence used to estimate the jaguar population includes footprints and reports of sightings by local humans. Suggest one disadvantage of each of these methods for estimating the size of the jaguar population. [2 marks]

Human sightings - they may lie about the sighting Footprints - they can fade over time or due to the weather

The Madidi National Park is also home to approximately 260 000 humans who support themselves by means of cattle-farming, and the production of timber and brazil nuts (a large nut harvested from a local native tree). Conservationists have been working with: * local people to promote sustainable use of these resources; and * government agencies to maintain the quality of the national park. Explain why the Madidi National Park is an example of conservation rather than preservation. [3 marks]

- local people are there - sustainable use - logging/ farming

The potato plant, Solanum tuberosum, is a staple food plant in many parts of the world. Potatoes are susceptible to infection by a pathogen called Phytophthora infestans, which causes a disease known as potato late blight. The most visible sign of the disease is a brown discolouration of the leaves. Some varieties of potato are resistant to infection by P. infestans. State two ways in which an individual S. tuberosum plant could respond to infection by P. infestans. [2 marks]

- they could drop any infected leaves (abscission) - they could release chemicals which help to prevent the spread of the pathogen

Describe two differences between the two images that could have been used to classify humans and chimpanzees in separate families. [2 marks]

- chimpanzees have a very short thumb whereas humans have a longer one (more proportional to its fingers) - chimpanzees have a longer palm than humans

Some scientists have suggested that humans and chimpanzees should be reclassified as belonging to the same genus. Evaluate their suggestion using evidence from Figs. 19.1 to 19.3 and your own knowledge of the scientific basis for the classification of organisms. [6 marks]

Reasons for: - the two species only diverged very recently, which can be seen by the value on thee x-axis being just after 5 Reasons against: - different anatomy between the two species, which can be seen in differences like thumb size in the figure - they still belong to the same branch on the phylogenetic tree

One type of gene is known as a homeobox gene. The base sequences of homeobox genes in humans and chimpanzees are almost identical. What conclusions about the evolutionary relationship between humans and chimpanzees can be drawn from this piece of evidence? [1 mark]

No - homeobox genes are conserved

Another disaccharide is maltose. Maltose and lactose both contain the same number of atoms of each element, C, H and O. State two other structural similarities between lactose and maltose. [2 marks]

- both contain a 5-carbon ring - both contain only one oxygen atom in the carbon ring

Explain how the structure of galactose allows it to be used as a respiratory substrate. [3 marks]

- bonds contain energy - broken by enzymes - soluble so can move throughout the cell

E. coli usually grows in conditions where the extracellular concentration of lactose is low. In such conditions lactose does not easily cross the bacterial cell surface membrane. Suggest and explain why lactose is unable to cross membranes. [2 marks]

- too big - cannot pass between phospholipids

In order for lactose to enter the cytoplasm of E. coli a protein is required. The E. coli living in the digestive system of young mammals are more likely to contain this protein than E. coli living in the digestive system of old mammals. Suggest an explanation for this observation. [2 marks]

- high lactose concentration - gene for the protein channel is switched on

Lactose is a reducing sugar. Benedict’s reagent can be used to detect the presence of lactose in a solution. A colorimeter can be used to measure the concentration of lactose. The colorimeter first needs to be calibrated. Describe how a method that uses Benedict’s reagent and a colorimeter. [4 marks]

- zero colorimeter - using blank - use red filter - serial dilutions - draw calibration curve

A ratio that is different from the expected 9:3:3:1 in a cross such as this can be the result of epistasis. Suggest and explain one reason, other than epistasis, why the phenotype ratio might not be 9:3:3:1. [3 marks]

- linkage - alleles are only a short distance apart, so they both appear on the same chromosome - no independent assortment

The yellow colour in peas is the results of an enzyme that breaks down chlorophyll, which is green. The Y allele codes for the production of an enzyme that breaks down chlorophyll. The y allele is the results of a mutation and codes for an inactive form of this enzyme. Outline how the Y allele codes for the production of this enzyme and explain why the y allele codes for an enzyme with a different primary structure. [6 marks]

Genetic code - - DNA sequence codes for amino acid sequence Transcription - - complementary base pairing - synthesis of mRNA strand Translation - - mRNA attaches to the ribosome - tRNA and mRNA synthesis the amino acid - a polypeptide is then formed in the golgi apparatus Effect of y - - different mRNA and tRNA condon/anticodons - so a different amino acid is produced

TLC can also be used to separate photosynthetic pigments. State a material that can be used as the stationary phase in TLC. [1 mark]

Silica gel

State the precise location of photosynthetic pigments in a chloroplast. [1 mark]

Thylakoid membrane - photosystems

MS is an autoimmune disease that damages the nervous system. Suggest how the immune system causes damage to the nervous system. [2 marks]

- the antigens on the myelin sheath of neurones is detected as 'non-self' by the body's immune system - so antibodies that attack the myelin sheath are subsequently produced

Guillain–Barré syndrome is another autoimmune condition in which neurones are damaged and the rate of nervous impulses is reduced. MS affects the central nervous system. Guillain–Barré syndrome affects the peripheral nervous system. Suggest two symptoms of MS that might not be present in people with Guillain–Barré syndrome. [2 marks]

- a decreased ability in balance and coordination due to damage to the cerebellum - a decrease in memory capacity due to damage to the cerebrum

Multiple sclerosis and Guillain–Barré syndrome both cause muscle weakness and loss of muscle function. Suggest and describe how the function of neuromuscular junctions will be affected by multiple sclerosis and Guillain–Barré syndrome. [2 marks]

- there may be fewer action potentials generated - so less neurotransmitters diffuse into the synaptic cleft

Many organisms have evolved specialised gas exchange surfaces. One feature of these structures is their large surface area to volume ratio. Describe how the structures of the insect tracheal system and fish gills provide a large surface area for gas exchange. [2 marks]

Insect tracheal system - they have tracheoles which are highly branched structures Fish gills - they have lots of folded filaments

The lugworm, Arenicola marina, is a species of segmented worm that lives in burrows in damp sand. They have hair-like external gills that increase the surface area available for gas exchange. Many other species of segmented worm do not have external gills. Suggest why lugworms have evolved external gills. [1 mark]

- the ability to access oxygen may be more difficult underground where the lugworm lives

Gestational diabetes is a medical condition that affects pregnant women. It results in high levels of glucose in the blood, even though the woman produces normal levels of insulin. Gestational diabetes is most similar to which type of diabetes? [2 marks]

- type two diabetes is the most similar - because whilst insulin is still being produced, the cells are no longer responding to it

Suggest two ways a woman with gestational diabetes can manage her condition. [2 marks]

- control diet - ensure it is low in carbohydrates - exercise regularly

Skeletal muscle is one of the main tissues where glucose is removed from the blood in response to insulin. Name the other tissue. [1 mark]

Liver tissue

Explain why glucose is required for the contraction of skeletal muscle. [3 marks]

- it is needed in respiration - to produce ATP - ATP is needed to break actin-myosin cross bridges

Outline the importance of photosynthetic pigments in photosynthesis. [4 marks]

- photosynthetic pigments like chlorophyll A absorb various wavelengths of light - which is needed to excite electrons - primary pigments are oxidised and pass electrons down the electron transport chain - this begins the LDR

Outline the role of membranes within cells. [2 marks]

- compartmentalisation - to separates the sites of chemical reactions

Give three properties of cellulose that make it suitable as the basis of plant cell walls. [3 marks]

1. insoluble in water 2. inert (don't react) 3. very flexible

Cellulose cannot be digested by animals. Some mammals have bacteria in their stomachs that produce enzymes that digest cellulose. Explain whether the action of these enzymes is intracellular or extracellular. [1 mark]

- extracellular - the enzymes are produced in the bacterial cells but leave to be used in the stomach

A common cause from TTX poisoning is suffocation ass a result of paralysis of the diaphragm. Explain how paralysis of the diaphragm could lead to suffocation. [2 marks]

- the diaphragm moves up and down to increase and decrease the volume of the thoracic cavity - but this cannot happen in paralysis, so less air gets into and out of the lungs, causing suffocation

TTX is also known to reduce the speed of conductioin in the Purkyne fibres of the heart. Suggest and explain what effect this would have on the heart rate. [3 marks]

- heart rate would decrease - because it would take longer for the electrical impulse to cause the ventricles to contract - and the heart spends more time in diastole - so the time taken for the heart to repolarise is longer, reducing the number of heart beats per minute