iGCSE 0654 - Paper 13 Summer 2019

• A

• B

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• C

Answer explanation

All organisms share the same 7 processes:

Movement

Reproduction

Sensitivity

Growth

Respiration

Excretion

Nutrition

From the answers available, all organisms are sensitive to changes.

All living organism excrete waste, but not always solid. For example, plants excrete oxygen as a gas through photosynthesis.

Producers do not feed on other living organisms. Only consumers do. Producers photosynthesise to get their nutrition.

Alternative D might be seen as correct, but not all organisms increase their cell number.

• A

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• D

Answer explanation

The blood capillary is delivering to the cell what is necessary for respiration to happen, i.e. the reactants.

The reactants in respiration are glucose and oxygen, producing carbon dioxide and water. The carbon dioxide and water diffuse back into the blood (the products of respiration).

The carbon dioxide will reach our lungs, diffuse into the alveoli and will be breathed out/exhaled.

• A

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• D

Answer explanation

Both carbohydrates and fats are composed of the same three elements: Carbon, Hydrogen and Oxygen. Excess carbohydrates can be stored as fat, and stored fat can be converted into carbohydrates by the liver (for energy).

Proteins contain nitrogen, as well as the other three elements. An example is that plants require nitrates NH₃^- ions from the soil. Together with glucose (a carbohydrate), the plant makes an amino acid, which then forms protein to aid in the growth of the plant.

• A

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• D

Answer explanation

The question specifies that we are dealing with a human/mammalian (mammal) enzyme. This means that the optimal temperature (the best temperature) with which the enzyme will work is 37^oC. This is true for all mammals.

Fun fact: During digestion, reptiles need to be in a warm place, so that the enzymes in their digestive system work best. Remember that reptiles are cold-blooded animals.

• A

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• D

Answer explanation

In general, plants will use carbon dioxide from the air in order for photosynthesis to happen. In the process of photosynthesis, a molecule of six molecules of CO₂ will react with six molecules of water to produce six molecules of O₂, and one molecule of glucose C₆H₁₂O₆.

A lot of the glucose in plants will be used, together with nitrates, to form amino-acids and thus proteins. This removes carbon from the atmosphere.

• A

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• D

Answer explanation

As we take in nutrients, it follows a very specific order:

Ingestion -> Digestion -> Absorption - > Assimilation -> Egestion

In ingestion, food in taken into the body through the mouth. In the mouth, it is then chewed (mechanical digestion) and mixed with amylase (to break down starch). The food is then swallowed along the oesophagus to the stomach. The stomach contains acid (to kill bacterias in the food) and other gastric juices (which contain enzymes to break down proteins).

Further break down of food happen in the small intestine, where food mixes with pancreatic juices for further breakdown and absortion through the villi. The main function of the villi is to increase the surface area of the small intestine for better absorption.

In the villi, fats (fatty acids and glycerol) are absorbed by the lacteal and other nutrients are absorbed into the hepatic portal vein towards the liver.

Any undigested nutrient goes to the large intestine, where water is reclaimed by the body and the faeces are stored until egestion happen.

• A

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• D

Answer explanation

Our transport/vascular system is a one-way path. It only allows blood to travel in a specific direction.

In a very simple way, blood from our body end up at the vena cava, which then travels towards the heart. In the heart, it is pumped through the pulmonary artery into the lungs. From the lungs, the blood travels back into the heart through the pulmonary vein and, finally, away from the heart to the rest of the body through the aorta (an artery).

If this was not the case, several different things could be happen, such as oxygen-poor blood never reaching the lungs or oxygen-rich blood only reaching certain parts of the body.

A simple difference between veins and arteries?

Veins have thin walls and carry blood towards the heart.

Arteries have very thick walls and carry blood away from the heart. The walls have to be think, as the pressure of the blood is much higher to reach the lungs and the rest of our body.

• A

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• D

Answer explanation

Remember the meaning of inspired and expired air. Inspire means breath in (oxygen-rich air) and expire means breath out (carbon dioxide rich air).

Once expired air dissolves in limewater (Ca(OH)₂), it will turn the limewater from clear to milky, due to the fact that expired air ir rich in carbon dioxide.

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• D

Answer explanation

A complete reflex arc follows a particular path:

A stimulus is sensed by the receptor (an organ such as a the eye or the skin). The receptor will send an impulse to the central nervous system along the sensory neurones. The central nervous system will send an impulse to the effector (a muscle, for example) along a motor neurone to act on that initial stimulus.

So:

Stimulus -> receptor -> Sensory Neurone -> Central Nervous System -> Motor Neurone -> Effector -> Response

• A

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• D

Answer explanation

The flower is divided into male and female parts.

The male part of the flower contains the anther, where pollen is found, and a filament holding the anther up. These form the stamen.

The female part of the flower contains the stigma, where the pollen lands and gets stuck, the style, through which the pollen tube grows, and the ovary, containing the ovules that are going to be fertilised by the information in the pollen. These form the carpel.