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Question Video: Understanding The Process By Which Ions Move Against Their Concentration Gradients Biology

The graph shows a comparison between the cells of the algae 𝑁𝑖𝑡𝑒𝑙𝑙𝑎 and the surrounding water. By what process could the 𝑁𝑖𝑡𝑒𝑙𝑙𝑎 obtain more calcium (Ca²⁺) from the surrounding water?

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Video Transcript

The graph shows a comparison between the cells of the algae Nitella and the surrounding water. By what process could the Nitella obtain more calcium, Ca2+, from the surrounding water?

Plants and algae, like the species that belong to the Nitella genus pictured here, must obtain many of their nutrients from their surroundings. Algae like Nitella live in aquatic environments, so they absorb nutrients from the surrounding water. There are two major ways in which mineral ions like calcium can be absorbed into the algae cells. Diffusion is the movement of particles from an area of high concentration to an area of low concentration, sometimes described as down or along a concentration gradient. For example, if calcium ions were in a higher concentration in the surrounding water outside the Nitella cells, they would move into the Nitella cells via diffusion passively without using an input of energy.

Active transport, however, is the movement of particles up or against their concentration gradient from an area of low concentration to an area of high concentration. Active transport, as the name suggests, is an active process, so it requires an input of energy to occur. If the concentration of ions is higher inside the Nitella cells than it is in the surrounding water, these ions will need to move by active transport into the cell using an input of energy from the organism itself.

If we take a look back at the graph, we can see that the concentration of calcium ions is higher within the Nitella cells than it is in the surrounding water. However, the algae may still require more calcium ions to carry out essential life processes. To obtain more calcium ions, the plant would need to move them against their concentration gradient from an area of low concentration outside the cell in the surrounding water to an area of comparatively higher concentration inside the cells. As we’ve just seen, the way they do this is using active transport. So we’ve deduced that the method Nitella cells could use to absorb more calcium from the surrounding water is active transport.

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