Cells, Body Systems & Nutrition

Which piece of equipment is used to observe the structure of individual cells in a school laboratory?

• AA barometer
• BA light microscope✓
• CA telescope
• DA thermometer

Answer: A light microscope magnifies a thin sample enough for individual cells to be seen and their structures identified. Telescopes are designed to view distant objects such as stars, not microscopic structures. A barometer measures air pressure and a thermometer measures temperature, so neither can reveal cell structure.

What is the main function of the nucleus in a cell?

• AIt controls the cell's activities and contains its genetic information✓
• BIt stores cell sap to help keep the cell firm and rigid
• CIt absorbs light energy from sunlight to make food for the whole plant cell
• DIt breaks down food molecules to release energy for use by the whole cell

Answer: The nucleus contains the cell's genetic information and directs the activities that take place inside the cell. Absorbing light to make food is the job of chloroplasts, not the nucleus. Storing cell sap is the role of the vacuole, and releasing energy from food is carried out by mitochondria.

What is the main function of the cell membrane?

• AIt contains the cell's genetic information
• BIt gives rigid structural support to plant cells
• CIt converts light energy into chemical energy
• DIt controls which substances enter and leave the cell✓

Answer: The cell membrane surrounds the cell and controls the movement of substances into and out of it. Rigid structural support in plant cells is provided by the cell wall, not the membrane. Genetic information is held in the nucleus, and converting light energy into chemical energy is the job of chloroplasts.

Which cell structure releases energy from food during respiration?

• AMitochondria✓
• BRibosomes
• CCell membranes
• DVacuoles

Answer: Mitochondria are the site of respiration, the process that releases energy from food for the cell to use. Cell membranes control which substances enter and leave the cell, which is a different job entirely. Ribosomes build proteins rather than releasing energy, and vacuoles store cell sap rather than producing energy.

Which structure is found in plant cells but not in animal cells, giving the cell a fixed shape?

• AA dense network of mitochondria
• BA rigid cell wall made of cellulose✓
• CA flexible cell membrane
• DA large permanent nucleus

Answer: Plant cells have a rigid cell wall made of cellulose surrounding the cell membrane, which gives the cell a fixed shape and support; animal cells lack this structure. Both plant and animal cells have a flexible cell membrane, so this cannot be the difference. Both cell types also contain a nucleus and mitochondria, so these are not unique to plants either.

What is diffusion, as it applies to the movement of substances in and between cells?

• AThe bulk flow of a liquid or gas moving through a narrow tube, driven by a difference in pressure on either side
• BThe net movement of particles from an area of higher concentration to an area of lower concentration✓
• CThe net movement of particles from an area of low to high concentration
• DThe active transport of particles against a concentration gradient, using energy released during respiration

Answer: Diffusion is the net movement of particles, such as oxygen or dissolved substances, from a region where they are more concentrated to a region where they are less concentrated, and it needs no extra energy input. Active pumping using energy is a different process called active transport, not diffusion. Movement from low to high concentration is the opposite of diffusion, and bulk flow through a tube describes something else entirely.

What is the correct order of organisation in a multicellular organism, from smallest to largest?

• ACells, tissues, organs, systems, organism✓
• BSystems, organs, tissues, cells
• CTissues, then cells, systems, then organs, then organism
• DOrgans, then tissues, cells, then organism, then systems

Answer: In a multicellular organism, cells group together to form tissues, tissues form organs, organs form systems, and systems work together to make up the whole organism. Placing tissues before cells reverses the first step of this sequence. Starting with organs or systems skips the smaller levels of organisation that build up to them.

Besides support, protection and movement, what other important job does the human skeleton do?

• AIt stores extra oxygen in muscles for use during exercise
• BIt produces enzymes for digesting food
• CIt controls heart rate and breathing rate during exercise
• DIt makes blood cells inside the bone marrow✓

Answer: Certain bones contain bone marrow, which produces the body's blood cells. Oxygen is carried by red blood cells and stored temporarily in muscles, not made by bones for storage. Digestive enzymes are produced by digestive organs, and heart and breathing rate are controlled by the heart, lungs and nervous system, not the skeleton.

How does the rib cage help protect the body?

• AIt forms a flexible cushion that absorbs shock when walking
• BIt forms a hollow chamber that stores extra blood cells
• CIt forms a bony cage that shields the heart and lungs from injury✓
• DIt forms a bony cage that shields the stomach and liver from injury

Answer: The rib cage is made of curved bones that surround and shield the heart and lungs, the delicate organs in the upper chest. The stomach and liver sit lower in the abdomen and are not enclosed by the ribs. Absorbing shock when walking is a job for the leg joints, and blood cells are made in bone marrow, not stored in a chamber.

Which function of the human skeleton allows the body to stand upright and gives it its overall shape?

• AProviding protection
• BAiding circulation
• CProviding support✓
• DAllowing body movement

Answer: The skeleton provides a rigid framework that supports the body's weight, holds it upright and gives it its overall shape. Protection refers to bones shielding delicate organs, which is a separate function. Movement describes bones and muscles working together to move body parts, and circulation is carried out by the heart and blood vessels, not the skeleton.

The biceps and triceps in the upper arm are an example of what kind of muscle arrangement?

• AA synergistic pair, where both muscles contract together
• BAn antagonistic pair, where one muscle contracts as the other relaxes✓
• CA pair of muscles that are never attached to the same bone
• DA single muscle that both bends and straightens the arm

Answer: The biceps and triceps form an antagonistic pair: when the biceps contracts to bend the arm, the triceps relaxes, and when the triceps contracts to straighten the arm, the biceps relaxes. They do not contract together, which rules out a synergistic pairing. They are two separate muscles rather than one, and both are in fact attached to the bones of the arm so that they can move it.

What is true about how a skeletal muscle can move a bone?

• AA muscle can only pull on a bone by contracting; it cannot push✓
• BA muscle moves a bone only by stretching outward, never by contracting inward
• CA muscle can either push or pull on a bone, depending on the movement being made
• DA muscle moves a bone by changing the bone's own shape

Answer: A skeletal muscle can only pull a bone by contracting and getting shorter; it cannot actively push, which is why muscles work in pairs to move a joint both ways. Muscles cannot push on bones, so the claim that they can do both is incorrect. It is contraction, not stretching, that produces the pulling force, and muscles move bones by pulling on them rather than changing the bone's own shape.

How could a pupil measure the force exerted by their arm muscles in a school investigation?

• ABy measuring the temperature change in the arm muscle
• BBy timing how quickly the arm can lift a fixed weight
• CBy pulling on a newton meter and reading the force in newtons✓
• DBy counting how many times the arm can bend in a minute

Answer: A newton meter measures force directly in newtons, so pulling on one with an arm muscle gives a direct reading of the force exerted. Timing a lift measures speed, not force, and counting repetitions measures endurance rather than the size of the force. Measuring a temperature change relates to energy release, not to the force a muscle produces.

Why does the human body need carbohydrates in its diet?

• AThey are needed mainly to protect the body from infection
• BThey are needed mainly for growth and repair of tissues
• CThey are needed mainly to carry oxygen around the body
• DThey are the body's main source of energy✓

Answer: Carbohydrates, such as starch and sugar, are broken down to release energy and are the body's main energy source. Growth and repair of tissues is mainly the job of proteins, not carbohydrates. Carrying oxygen is done by red blood cells, and protecting the body from infection is a role of the immune system, not a nutrient group.

Why does the human body need protein in its diet?

• AAs the body's preferred first source of energy
• BTo dissolve fat-soluble vitamins for absorption
• CTo provide the body with dietary fibre
• DFor growth and repair of body tissues✓

Answer: Proteins are used by the body to build and repair tissues such as muscle, which is why growing children need plenty of protein. Carbohydrates, not protein, are the body's preferred first energy source. Dietary fibre comes from plant material rather than protein, and dissolving fat-soluble vitamins is not a function of protein in the diet.

How is the lining of the small intestine adapted for absorbing digested food?

• AIt is coiled tightly, which reduces its overall surface area
• BIt is lined with tough enamel that increases its surface area
• CIt is covered in tiny finger-like villi that increase its surface area✓
• DIt is covered in a thick layer of muscle that increases its surface area

Answer: The lining of the small intestine has millions of tiny, finger-like villi, which greatly increase its surface area so that digested food can be absorbed efficiently into the blood. The increased surface area comes from villi, not from an extra layer of muscle. Enamel is found on teeth, not intestines, and the intestine is coiled to fit inside the body, not to reduce its surface area.

What can a long-term lack of vitamin C in the diet lead to?

• ADiabetes, linked to sugar levels
• BObesity, caused by excess energy intake
• CRickets, caused by a lack of vitamin D
• DScurvy, a deficiency disease✓

Answer: A long-term lack of vitamin C causes scurvy, a deficiency disease that affects the skin, gums and blood vessels. Obesity results from eating more energy than the body uses, not from a shortage of vitamin C. Rickets is caused by a lack of vitamin D, and diabetes is linked to how the body handles sugar, not vitamin C intake.

A pupil's recommended daily energy intake is 9,000 kJ. One portion of pasta provides 1,500 kJ. What fraction of the pupil's daily energy intake does one portion provide?

• AOne quarter
• BOne third
• COne sixth✓
• DOne half

Answer: 1,500 kJ divided by 9,000 kJ simplifies to one sixth, so one portion of pasta supplies one sixth of the recommended daily energy intake. One third would require the portion to provide 3,000 kJ, which is double the actual value. One quarter and one half are even larger fractions and would need portions of 2,250 kJ and 4,500 kJ, both far more than 1,500 kJ.

What role do enzymes play in the digestive system?

• AThey act as biological catalysts that speed up the breakdown of food✓
• BThey store the energy released from digested food
• CThey physically grind food into smaller pieces in the stomach
• DThey act as biological catalysts that slow down the breakdown of food

Answer: Enzymes are biological catalysts that speed up the chemical breakdown of large food molecules into smaller ones the body can absorb. They speed up digestion rather than slowing it down, so the opposite claim is incorrect. Storing energy is not what enzymes do, and physically grinding food is a mechanical process carried out by the teeth and stomach muscles, not by enzymes.

Why are bacteria in the human digestive system important?

• AThey replace the digestive enzymes made by the pancreas
• BThey help digest some foods that the body cannot break down alone✓
• CThey destroy the nutrients present in digested food
• DThey stop the small intestine from absorbing water

Answer: Bacteria living in the digestive system, particularly in the large intestine, help to break down certain foods, such as some plant fibre, that the body's own enzymes cannot fully digest. Far from destroying nutrients, these bacteria help release nutrients from food. They work alongside digestive enzymes rather than replacing them, and they do not prevent the small intestine from absorbing water.

How are the alveoli in human lungs adapted for efficient gas exchange?

• AThey have thin walls but a very small total surface area
• BThey have thin walls and a large total surface area, with a good blood supply✓
• CThey have a large surface area but no blood supply at all
• DThey have thick walls and a small total surface area, with a poor blood supply

Answer: Alveoli have very thin walls, an enormous combined surface area, and a rich network of blood capillaries, all of which let oxygen and carbon dioxide diffuse quickly between air and blood. Thick walls and a poor blood supply would slow diffusion rather than speed it up. A small surface area would also limit the rate of gas exchange, and without a blood supply, gases could not be carried away from the alveoli at all.

What happens to the rib cage and diaphragm when a person breathes in?

• AThe rib cage stays still while the diaphragm flattens and moves down
• BThe rib cage moves up and out, and the diaphragm flattens and moves down✓
• CThe rib cage moves up and out while the diaphragm domes and moves up
• DThe rib cage moves down and in, and the diaphragm domes and moves up

Answer: During breathing in, the rib cage moves up and outwards and the diaphragm contracts, flattening and moving downwards, which increases the volume of the chest and draws air into the lungs. The reverse movements, with the rib cage moving down and the diaphragm doming upwards, happen during breathing out instead. The rib cage does move during breathing rather than staying still, and it moves out rather than in while the diaphragm flattens.

How could lung volume be simply measured in a school investigation?

• ABy simply counting the total number of breaths a pupil takes in one full minute
• BBy carefully measuring the pupil's chest circumference with a tape measure
• CBy breathing out fully into a container and measuring the air displaced✓
• DBy simply measuring the pupil's height while standing upright against a wall

Answer: A simple way to estimate lung volume is to breathe out fully into a container, such as a bag or a water-filled vessel, and measure the volume of air that is displaced. Chest circumference relates to body size rather than to the volume of air the lungs can hold. Counting breaths per minute measures breathing rate, not lung volume, and height is not a direct measurement of lung capacity either.

What effect does smoking have on the human gas exchange system?

• AIt damages the airway lining and reduces the efficiency of gas exchange✓
• BIt only affects the sense of taste, not the airways or lungs
• CIt has no measurable effect on the airways or gas exchange
• DIt strengthens the airway lining and improves the efficiency of gas exchange

Answer: Smoking damages the delicate lining of the airways and alveoli, reducing how efficiently oxygen and carbon dioxide can be exchanged and increasing the risk of diseases such as bronchitis. It weakens rather than strengthens this lining, so the opposite claim is incorrect. Smoking does have well-documented effects on the airways, and those effects go well beyond taste to include serious damage to the lungs themselves.

What happens to the airways during an asthma attack?

• AThe airways widen, making it easier to breathe
• BThe airways narrow, making it harder to breathe✓
• CThe airways swap places entirely with the blood vessels
• DThe airways fill up permanently with solid bone tissue

Answer: During an asthma attack, the muscles around the airways tighten and the lining becomes inflamed, narrowing the airways and making it harder for air to flow in and out. The airways narrow rather than widen during an attack, which is why breathing becomes more difficult, not easier. Airways do not fill with bone tissue, and airways and blood vessels are separate structures that cannot swap places.

What is the role of stomata in a plant leaf?

• AThey are solid cells that store starch made during photosynthesis
• BThey are pores that allow gases to move in and out of the leaf✓
• CThey are waxy patches that stop any gases entering or leaving the leaf
• DThey are pores that allow water to be pumped directly into the roots

Answer: Stomata are tiny pores, mostly on the underside of a leaf, that allow gases such as carbon dioxide and oxygen to diffuse in and out during photosynthesis and respiration. They are not involved in pumping water into the roots, which happens elsewhere in the plant. Stomata are pores rather than solid storage cells, and their function is to let gases pass through the leaf, not to block them.