Question Video: Explaining the Location of Palisade Cells in the Leaf | Nagwa Question Video: Explaining the Location of Palisade Cells in the Leaf | Nagwa

Question Video: Explaining the Location of Palisade Cells in the Leaf Biology • Second Year of Secondary School

Palisade cells near the top of the leaf contain many chloroplasts. Which of the following best explains why? [A] Palisade cells contain many chloroplasts to capture the sunlight needed for respiration. [B] Palisade cells contain many chloroplasts to allow the maximum diffusion of gases. [C] Palisade cells contain many chloroplasts to expand the cell and increase the surface area available for water uptake. [D] Palisade cells contain many chloroplasts to capture the sunlight needed for photosynthesis.

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Video Transcript

Palisade cells near the top of the leaf contain many chloroplasts. Which of the following best explains why? (A) Palisade cells contain many chloroplasts to capture the sunlight needed for respiration. (B) Palisade cells contain many chloroplasts to allow the maximum diffusion of gases. (C) Palisade cells contain many chloroplasts to expand the cell and increase the surface area available for water uptake. (D) Palisade cells contain many chloroplasts to capture the sunlight needed for photosynthesis.

Since the question uses the term leaf, we know that we’re dealing with a plant. And it mentions a type of cell that’s found in the leaf. So we’ll need to know about some plant cells as well. Another key term in the question is chloroplasts. Chloroplasts are organelles, and organelles are structures and cells that are responsible for specific functions. Let’s take a look at the terms and the solution options to see what else we need to know about these plant cells.

Option (A) contains the term respiration, and respiration occurs in an organelle called the mitochondrion. Option (B) mentions the diffusion of gases between the interior of a leaf and the environment, which occurs through a structure called a stoma that’s formed by two guard cells. Option (C) contains the term water uptake, but that actually occurs in the roots, especially through some tiny structures called root hairs that increase the surface area where water uptake occurs. Option (D) mentions the process of photosynthesis. And photosynthesis can be summarized by the equation below, where carbon dioxide and water react using the energy in sunlight to form sugar and oxygen.

So let’s make some connections between these structures on our diagram. First, water is taken up by the root hairs. It moves through a tissue called the xylem, where it finally gets to the leaf. As long as there’s enough water in the guard cells of the stoma, they’ll stay expanded, which keeps the stoma open for gas exchange, including the diffusion of CO2 from the atmosphere down its concentration gradient into the area of the leaf known as the spongy mesophyll. Plants use the carbon dioxide and water in the process of photosynthesis to make sugar and oxygen. The sugar can be used by the mitochondria in the process of cellular respiration. The oxygen can be used by the mitochondria in cellular respiration, or it can exit into the atmosphere by diffusing down its concentration gradient.

So option (A) must be incorrect because cellular respiration occurs in the mitochondria and not in the chloroplasts. Option (B) is incorrect because the diffusion of gases takes place in the plants’ stomata located on the underside of their leaves. And option (C) is incorrect because water uptake occurs in the root hairs, not in the chloroplasts. Option (D) says that chloroplasts capture sunlight that’s needed for the process of photosynthesis. And that is indeed true. That’s what happens in the chloroplast.

It’s interesting to note though that we didn’t even have to know what a palisade cell was to be able to answer this question correctly. So if you don’t know a term in a question, don’t let it scare you away. Look at the rest of the question and try to figure out what you can. On the other hand, it’s even better to know what a palisade cell is. Palisade cells make up the palisade mesophyll tissue, which is directly beneath the epidermis and cuticle on the top of the leaf. And they contain many chloroplasts. And the tissue beneath the palisade mesophyll is called the spongy mesophyll. It’s called spongy because there’s a lot of air pockets, and that allows the gases to diffuse through.

So the answer to the question “Palisade cells near the top of the leaf contain many chloroplasts. Which of the following best explains why?” is option (D). Palisade cells contain many chloroplasts to capture the sunlight needed for photosynthesis.

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