Seconday 5 (MYE) - Essay (6)

6. (a) Based on your knowledge in Biology and Diagram 13, explain the uptake of water from the soil to the leaves. Your answer should include all the mechanisms/processes that facilitate the uptake of water in plants. [8 marks]

Diagram 13











The cytoplasm of root hair cells is usually hypertonic to the surrounding soil water [1]
Hence, water enters the root hair cells by osmosis [1]
The root hair cells are now hypotonic to the adjacent root cortex cells [1]
Water then diffuses into these cells until it reaches the cortex region [1]
Water flows through the parenchyma cells (cortex) until it reaches the endodermis through either the apoplastic pathway or the symplastic pathway [1]
The Casparian strips (impermeable to water) prevent water from moving through the cell wall of the endodermal cells [1]
The water concentration gradient which exists across the cortex creates a transpiration pull to direct water into the xylem vessels [1]
Water finally reaches the mesophyll cells in the leaves where it will be lost through the stomata into the surroundings [1]
The upward movement of water through the xylem vessels in the stems to the stomata is also assisted by the root pressure, adhesion and cohesion [1]
Any 8


(b) For each type of food in Diagram 14 below explain how the concept of osmosis can be used in food preservation. [8 marks]

Diagram 14 - FISH, CARROTS

· Fish can be preserved by dehydration [1]
· Fish is smoked or dried under the sun to remove water [1]
· Fish can also be dried by adding salts which causes water to diffuse out from fish into hypertonic surrounding [1]
· Dehydrated fish has low water content that prevents growth of microbes [1]

· Carrot strips are soaked in a vinegar syrup solution [1]
· The cell sap of the carrot cells is hypotonic to the external solution [1]
· Water diffuses out of the carrot cells into the hypertonic surroundings [1]
· The dried and shrunk carrot strips prevent the growth of microbes [1]


Most green plants do not have woody stems to hold them up, but depend on turgidity of cells.

(c) Based on the statement above, explain what will happen to a herbaceous plant or a freshly picked flower if it is kept out of water. [4 marks]

· Support in most green plants such as herbaceous plants is supported by turgidity of the parenchyma and collenchyma cells [1]
· Water diffuses into the vacuole of the plant cells throught osmosis [1]
· The developed turgor pressure of fluids in the central vacuole pushes the protoplasm and plasma membrane against the cell wall [1]
· This creates support for the stems, roots and leaves [1]