[Biology] Chapter 2: Movement of Substances

Comprehensive practice questions covering the definitions, examples, and factors affecting diffusion, osmosis, and active transport based on the lecture notes.

What is the definition of diffusion?

The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient.

What is the definition of osmosis?

The net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane.

What is the definition of active transport?

The movement of particles, using energy, from a region of lower concentration to a region of higher concentration, against a concentration gradient, through a partially permeable membrane.

How do glucose and amino acids enter the epithelial cells of villi in the small intestine after diffusion no longer occurs?

They are transported in via active transport.

How do mineral salts enter root hair cells from the soil, and why?

Via active transport, to maintain a high concentration of mineral salts in their vacuoles.

Why does water flow into root hair cells by osmosis?

The active transport of mineral salts into the vacuoles creates a region of lower water potential than the surrounding soil.

Describe the process of $O_2$ entering the blood from the alveoli.

$O_2$ dissolves into the thin film of moisture lining the alveolar air space, then diffuses into the blood plasma.

In which direction does $CO_2$ diffuse during gas exchange in the lungs?

From the blood plasma into the alveoli air space.

How do $O_2$ and $CO_2$ move through the stomata of a leaf?

$O_2$ diffuses from the intercellular air spaces to the surrounding air, while $CO_2$ diffuses from the surrounding air into the intercellular air spaces.

What happens to an animal cell placed in a solution with high water potential?

It bursts/lyses.

What happens to an animal cell placed in a solution with low or very low water potential?

It becomes crenated.

What is the effect on a plant cell when placed in solutions of high, low, and very low water potential respectively?

High: Turgid; Low: Flaccid; Very Low: Plasmolysed.

What specifically happens to a plant cell during plasmolysis?

Water molecules leave the cell sap from the large central vacuole by osmosis, causing the cytoplasm to shrink until the cell membrane pulls away from the cell wall.

Why is turgidity important for plants with non-woody stems?

It allows the plant to remain upright and reach for sunlight.

How does the surface area to volume ratio ($SA:V$) affect the rate of diffusion?

The higher the $SA:V$, the higher the diffusion rate.

How does temperature affect the rate of diffusion?

Higher temperature gives molecules more kinetic energy, so they move and diffuse down the concentration gradient faster.

How do the 'steepness' of the concentration gradient and 'diffusion distance' affect the diffusion rate?

A steeper gradient and a shorter diffusion distance both lead to a higher diffusion rate.

Which molecule diffuses faster, glucose or sucrose, and why?

Glucose diffuses faster because smaller molecules diffuse faster.