The animal described, with skin with hairs and nourishing its young with milk, is a mammal.

Here are the answers to question 1.1:

1.1.1
The animal described, with skin with hairs and nourishing its young with milk, is a mammal.

• C

1.1.2
The left ventricle has the thickest wall because it pumps blood to the entire body.

• B

1.1.3
Biotic factors are living components of an ecosystem. Decomposers are living organisms.

• A

1.1.4
Bacterium X converts atmospheric nitrogen into nitrates in the soil, a process known as nitrogen fixation.

• C

1.1.5
According to the principle of superposition, older fossils are found in lower rock layers. Dinosaur bones are found above mollusc shells, making them younger.

• B

1.1.6
General diastole is the longest phase of the cardiac cycle, during which the entire heart relaxes and fills with blood.

• D

1.1.7
The structure labeled X is a valve, which prevents the backflow of blood, ensuring it flows towards the heart.

• D

1.1.8
The most energy is transferred when the food chain is shortest. Pathway D represents humans consuming green plants directly, which is the shortest chain.

• D