Transport

Unicellular organisms

Simple unicellular organisms rely on diffusion as the means by which molecules move in and out of their cells. This is because they have a high surface area to volume ration which results in diffusion occurring quickly.

Multicellular organisms

Multicellular organisms are simply too large for diffusion to occur efficiently. They have a small surface area to volume ratio. Therefore, multicellular organisms have elaborate systems such as the respiratory system and circulatory system to transport molecules around the body to support themselves.

Water moving into the roots

Water moves into the root hair cells through osmosis. When soils take in nutrients and minerals from the soil by active transport, a low water potential is created. This low water potential means that water would diffuse into the roots. The roots have a large surface area to volume ratio, to absorb minerals and water at the greatest rate possible.

Lack of minerals in the soil, waterlogged soil and leaves removed

Without minerals in the soil such as nitrates, a plant would wilt. Nitrates make up amino acids which form proteins. Without protein, a plant cannot grow and support itself hence it wilts. Without magnesium, chlorophyll cannot be produced and a plant cannot photosynthesise to create glucose for growth also. The plant would also turn yellow.

A water logged soil would cause nutrients to become diluted. Diluted nutrients are not concentrated hence they cannot be taken up into the plant by active transport. There is no oxygen in waterlogged soil for plants to respire from.

A plant with its leaves removed would not be able to absorb water through osmosis in the root hair cells as transpiration is not occurring and providing a low water potential.

Minerals, nutrients, dissolved solutes and water are stored in the vacuole in cells before they are taken up through the xylem and distributed to other areas of the plants. Glucose is transported through the phloem from the leaves [where it is produced from photosynthesis] to other areas of the plant.

Phloem and Xylem

There are two types of transport tissue in a plant:

1. Phloem
2. Xylem

1. The phloem transports glucose from the leaves of a plant [and any green area with chlorophyll] to the other areas. The phloem vessels are thin, permeable so that glucose can diffuse in and out. They transport glucose in both directions as every cell requires it for respiration. The thin walls are made from lignin. The phloem is involved in TRANSLOCATION. This defines the movement of food substances from the stem to growing tissues around the plant.

1. On the other hand, the xylem only flows upwards [one direction]. It consists of hollow tubes constructed of dead cells. The walls are thick and made from cellulose. They are impermeable to allow no water or minerals to diffuse out. They transport the water, minerals and nutrients from the roots to the leaves.