National 5 Biology | Unit 2 | Key Area 7: Absorption of Materials

Surfaces involved with the absorption of materials share the same features to maximise the efficiency of absorption. Name these three features.

- Large surface area

- Thin walls

- Extensive blood supply (consisting of extensive capillary networks to allow the exchange of materials at cellular level.)

Why can large animals not rely on diffusion for their gas exchange?

In large animals, the surface area becomes too small in relation to their mass. The distance to the cells in the centre of the organism becomes too great. Diffusion would be too slow.

What is the order of structures that air passes through as it enters the lungs?

Trachea → bronchus → bronchiole → alveolus

Describe what the trachea is and how air enters it.

The trachea (windpipe) connects the lungs to the outside of the body. It is strengthened by incomplete rings of cartilage. Air enters by passing by the larynx (voice box).

Bronchioles end in air sacs which consist of what?

Many alveoli (singular alveolus), which are extremely small, thin-walled structures.

Each lung is surrounded by two thin pleural membranes. The cavity between them is airtight and contains a thin layer of fluid. Name this fluid and its purpose.

The pleural fluid lubricates the lungs and reduces friction between the outer lung surface and the inside of the thorax during breathing movements.

The lungs are efficient gas exchange structures. Name five features that help it achieve this.

- Large surface area

- Moist inner surface of alveoli

- Thin walls (one cell thick)

- Good blood supply

- Steep concentration gradient maintained

The lungs are efficient gas exchange structures. How does a large surface area help?

Many alveoli provide a large surface area and allow large exchange surfaces for diffusion of oxygen and carbon dioxide.

The lungs are efficient gas exchange structures. How does moist inner surfaces of alveoli help?

The moist lining dissolves oxygen, helping it diffuse more efficiently.

The lungs are efficient gas exchange structures. How do thin walls help?

Walls that are only one cell thick provide a short pathway for diffusion to occur, making diffusion faster.

The lungs are efficient gas exchange structures. How does a good blood supply help?

Networks of capillaries cover alveoli to carry away oxygen and bring carbon dioxide from respiring tissues.

The lungs are efficient gas exchange structures. How does a steep concentration gradient help?

A continuous flow of blood ensures deoxygenated blood replaces oxygenated blood. This is combined with continuous breathing bringing fresh air. This maintains a steep concentration gradient, which increases the speed of diffusion.

Where are nutrients absorbed into the blood?

Nutrients from food are absorbed into the blood in the small intestine, when digested food molecules cross the wall of the gut and are absorbed into the blood or the lymphatic system by diffusion.

What substances are absorbed by the small intestine?

Glucose, amino acids, glycerol, fatty acids, water

The process of absorption in the small intestine is made an efficient process. What three main features help this?

- Extremely large surface area

- Thin epithelium

- Blood capillaries and lacteals

The process of absorption in the small intestine is made an efficient process. How is a huge surface area achieved?

- The small intestine is extremely long

- The walls of the small intestine are folded like a “concertina”

- Internal surface of the small intestine is covered in small projections called villi.

The process of absorption in the small intestine is made an efficient process. How does an extremely large surface areas help?

Provides a large area of contact between digested food and the absorbing surface, making diffusion quicker.

The process of absorption in the small intestine is made an efficient process. How does a thin epithelium help?

A thin epithelium provides a short diffusion pathway for digested food.

The process of absorption in the small intestine is made an efficient process. How do blood capillaries and lacteals in the villi (singular villus) help?

- Blood capillaries absorb glucose and amino acids

- Lacteals absorb glycerol and fatty acids (products of fat digestion)