IB Biology

A Unity and Diversity

A1.1 Water

A1.2 Nucleic acids

A2.1 Origins of cells

A2.2 Cell structure

A2.3 Viruses [HL only]

A3.1 Diversity of organisms

A3.2 Classification and cladistics [HL only]

A4.1 Evolution and speciation

A4.2 Conservation of biodiversity

B Form and Function

B1.1 Carbohydrates and lipids

B1.2 Proteins

B2.1 Membranes and membrane transport

B2.2 Organelles and compartmentalization

B2.3 Cell specialization

B3.1 Gas exchange

B3.2 Transport

B3.3 Muscle and motility [HL only]

B4.1 Adaptation to environment

B4.2 Ecological niches

C Interaction and Interdependence

C1.1 Enzymes and metabolism

C1.2 Cell respiration

C1.3 Photosynthesis

C2.1 Chemical signalling [HL only]

C2.2 Neural signalling

C3.1 Integration of body systems

C3.2 Defence against disease

C4.1 Populations and communities

C4.2 Transfers of energy and matter

D Continuity and Change

D1.1 DNA replication

D1.2 Protein synthesis

D1.3 Mutation and gene editing

D2.1 Cell and nuclear division

D2.2 Gene expression [HL only]

D2.3 Water potential

D3.1 Reproduction

D3.2 Inheritance

D3.3 Homeostasis

D4.1 Natural selection

D4.2 Stability and change

D4.3 Climate change

Question rangeC3.1.14—Heart rate feedback control

[Maximum number: 12]

A study was conducted to look at the short-term effects of a change in diet on the risk of disease in young adults. The table shows data on the habitual diet of the participants as well as the study diet followed for two weeks.

	Mean daily intake ± standard deviation
		Habitual diet	Study diet
Energy / kJ	$10143 \pm 949$	$9992 \pm 479$
Fat / g	$100 \pm 6$	$99 \pm 5$
Saturated fat / \% total fat	$37 \pm 2$	$60 \pm 1$
Unsaturated fat / \% total fat	$63 \pm 2$	$40 \pm 1$
Monounsaturated fat / \% total fat	$46 \pm 1$	$32 \pm 1$
Polyunsaturated fat / \% total fat	$17 \pm 1$	$8 \pm 1$
Carbohydrate / g	$248 \pm 23$	$232 \pm 16$
Protein / g	$119 \pm 12$	$120 \pm 9$

[Maximum number: 14]

Hypertension (blood pressure exceeding 140 mmHg ) affects millions of people worldwide. Many modern societies consume more sodium in the form of salt (NaCl) than is required for normal physiology. The effect of changing the levels of dietary sodium has been studied in various organisms.

Scientists recorded the blood pressure changes in chimpanzees (Pan troglodytes) fed a diet without added sodium (control) or a sodium supplemented diet (experimental) as follows
- 5 grams of salt per day from December 1991 until May 1992
- 10 grams of salt per day until June 1992
- 15 grams of salt per day until August 1993
after which no more salt was added to the diet until the experiment ended.

[Maximum number: 13]

Type II diabetes, a widespread and challenging health problem, is due to insulin resistance, which results in raised blood glucose. Alpha-glucosidase enzymes catalyse the hydrolysis of carbohydrates. Inhibition of the enzymes slows the absorption of glucose in the intestine and thus slows the rise in blood glucose. A study examined the inhibitory effect of five species of seaweed (Palmaria palmata, Saccharina latissima, Fucus vesiculosus, Ascophyllum nodosum and Alaria esculenta) on alpha-glucosidase. Dried seaweed extracts made with water or ethanol were added to maltose. The solutions were incubated, then analysed for glucose content.

The graph shows percent inhibition of alpha-glucosidase with different seaweed extracts compared with uninhibited enzyme activity (control).

[Maximum number: 9]

Angora rabbits (Oryctolagus cuniculus) have soft and silky coats with fine hairs that grow about 30 mm per month. These hairs can be collected and used as wool. Hair growth in mammals depends on stem cells in the base of hair follicles called dermal papilla cells.

Research was carried out to investigate the role of the WIF1 gene in hair growth. Wool was collected from 6-month-old angora rabbits. Expression of the WIF1 gene was assessed by measuring the quantity of WIF1 mRNA produced in cells taken from each rabbit. The rabbits were divided into groups according to their rate of wool production (low or high).

The table shows mean wool production per rabbit in the low and high wool production groups and relative expression of the WIF1 gene.

Removed for copyright reasons

A wearable monitor can be used to measure heart rate before and after exercise on an aerobic stepper. A student asked 100 female classmates of approximately 14 years of age to take part in the investigation.

monitor

stepper

[Maximum number: 3]

In an experiment to determine the effect of diet on response to leptin, mice were fed a control diet or a high fructose diet for six months and then either injected with a saline (salt) solution or injected with leptin. The food intake of both groups was then monitored over a 24 hour period.

[Maximum number: 7]

Aerobic capacity is a function of both $\mathrm{VO}_{2}$ max and heart beat rate. A study was conducted to see the effect of regular endurance exercise on maximal aerobic capacity in women. The scatter graphs show the effect of age on $\mathrm{VO}_{2}$ max and maximal heart rate for two groups of women. The endurance-trained group had been competing in long distance races for at least the past two years. The sedentary group performed no regular physical exercise but were healthy and non-obese.

B1. A study was carried out to assess the effects of high-intensity interval training on heart rate. 20 subjects were randomly assigned to two groups: training and control. They underwent a test in which the exercise became harder and harder until they reached the point of exhaustion (progressive incremental test). The training group then performed nine sessions of high intensity interval training on a cycle ergometer during three weeks ( 1 minute at 130 % of maximal aerobic work rate with 1 minute rest intervals until they felt they were at the point of exhaustion). The control group did not do any training. Both groups then repeated the progressive incremental test.

The graphs below show the mean heart rate curves during progressive incremental tests before and after training.