Answers to biology exercise

Question 1 ,[object Object],(R) Note: Structure R is referring to the Xylem Vessels, while Structure S is the phloem. There is a need to differentiate and remember the positions of the vessels in leaf, stem & root (Refer to your lecture slides)

Question 2 ,[object Object],(Prevents water loss) Note: Most of you answered this correctly Cuticle

Question 3 ,[object Object],(movement of manufactured food from the leaves to the rest of the plant ) Note: Most of you answered this correctly

Question 4 ,[object Object],(water and mineral salts) Note: All of you answered this correctly Do not confuse mineral salts with food substances such as sucrose and amino acids

Question 5 ,[object Object],(Root hairs) Note: Some of you answered this incorrectly. Root hairs are specialized structures that aid in absorption of water (Recall their adaptations) Epidermal cells do not directly participate in absorption of water & mineral salts as these cells become the tubular outgrowth of the root hairs

Question 6 ,[object Object],(Stomata) Note: Some of you answered this incorrectly. Transpiration in plants occur in the leaves as well as the stem. Leave – Stomata transpiration & Cuticular Transpiration (Cuticle does not totally prevent water loss) Stem – Lenticular transpiration (Lenticels are pores present on the stem which allow water vapour to move out of the stem) Minimal transpiration occurs through cuticular & lenticular transpiration (aids in cooling)

Question 7 ,[object Object],(only the aerial parts) Note: Most of you answered this incorrectly ( leaves ) See previous slide explanations. Not all parts of the plants allow transpiration, the roots do not transpire. They are adapted to water & mineral salts absorption. Aerial parts refer to the parts of plants above the ground excluding the roots.

Question 8 ,[object Object],(produce energy for translocation) Note: Some of you answered this incorrectly You need to know what companion cells are associated with, they are associated with phloem and contains many mitochondria. Transport of water in Xylem vessels does not require energy as there are forces which help to push (Root pressure), pull (Transpiration pull) & capillary action to direct water upwards the plant.

Question 9 ,[object Object],(high humidity) Note: Some of you answered this incorrectly Does not increase = decrease You need to understand which factor will cause the layer of air around the leaves to have higher water content, hence having a more gentle water potential gradient between the leaves and the surrounding atmosphere. With a gentle water potential gradient, water vapour cannot move out of the leaves as fast when compare to a steeper water potential gradient

Question 10 ,[object Object],(active transport) Note: Some of you answered this incorrectly ( diffusion, osmosis ) Recall root pressure – Dissolved mineral salts in the soil usually have lower concentration as compare the root cells. The root cells (root hair cells & cortical cells) are actively transporting mineral salts into the cortex and into the xylem vessels. Increase solute concentration = lower water potential within the root, hence water is able to enter the root through osmosis.

Question 11 ,[object Object],(turgor pressure of guard cells) Note: All answered this correctly.

Question 12 ,[object Object],(mainly lower surface) Note: Some of you answered this incorrectly (lower surface only) Please read the question properly. Sometimes, student makes mistake by rushing into the question without reading and understanding all the MCQ choices. Depending on the types of plant, stomata can also be found on the upper surface of leaves. However, for most land dicot plants, stomata are found mainly on the lower surface. What would happen if most of the stomata are found on the upper surface and are exposed to direct sunlight? Hint: Think about how transpiration will be affected.

Question 13 ,[object Object],Plants absorb water from the roots through the root hair cells that are elongated so as to increase surface area to volume ratio for faster absorption of water. This process is done through osmosis for water, while active transport for the mineral salts. For osmosis, water moves through a partially permeable membrane of the root hair cell down a concentration gradient, from high water potential to a low water potential. This is possible because the sap in the root hair cell is relatively concentrated with a solution mineral salts as they are actively transported into the root cells from the surrounding soil . Therefore, it creates a lower water potential, allowing water to enter. Now, the root hair cell has a high water potential compared to that of the next cell. Water moves through osmosis to the next cell and the process repeats. This process is known as root pressure.

Question 13 ,[object Object],Note: Include keywords such as osmosis for water and active transport for mineral salts. The question states movement of water within the root only, you do not need to mention capillary action and transpiration pull. It is good to mention that root hair helps to increase the rate of water absorption due to the large surface area to volume ratio

Question 14 ,[object Object],The leaf manufactures sucrose through photosynthesis. The sucrose is then transported into the phloem by active transport whereby energy is provided by the companion cells. The water potential in the phloem then become lower than that in the xylem, and hence water enters the phloem through osmosis. The sucrose mixes with the water and form a solution. It is then transported to the sink; where there is an increase demand for sucrose, via pressure flow. Sucrose is transported into the sink by active transport. Water is also attracted into the sink through osmosis which subsequently returned into the xylem vessels.

Question 14 ,[object Object],Note: Include keywords such as active transport of sucrose from the leaf into the phloem, pressure flow causes the movement of sucrose molecules to be transported to regions which demand sucrose Active transport must be mentioned when sucrose gets transported into the phloem from the source & from the phloem into the sink

Question 15 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Question 15 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Answers to biology exercise

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