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Lesson Video: Absorbing Minerals Biology

In this video, we will learn how to recall examples of micronutrients and macronutrients required by plants and explain how plants absorb these essential nutrients from the environment.

16:01

Video Transcript

In this video, we will land the distinction between macronutrients and micronutrients that are required by plants. We will discover the mechanisms by which plants absorb these essential nutrients to help them survive and practice applying our knowledge and graphical skills to some example questions.

All living organisms require some form of nutrients in order to survive. Nutrition is required for a vast array of functions in living things, such as to release energy, to provide materials for building up other substances for growth and repair of damaged tissues. And some nutrients are even involved in controlling some biological processes and ensuring that they function correctly.

Plants like this one will require some of their nutrition in the form of minerals. Minerals are inorganic nutrients that can’t be synthesized by an organism, so they need to be ingested or absorbed. Animals, like humans, are able to ingest their minerals and then absorb them across the wall of the digestive system. However, plants do not have a digestive system, so instead these minerals need to be taken in by absorption. Minerals can often be found in soil, and plants can absorb these nutrients from the soil, generally through their highly specialized root systems.

The biological molecules within the cells of all living things on Earth are largely made up of three key elements: carbon, hydrogen, and oxygen. In fact, carbohydrates, which are mainly used to release energy, include the word part carbo- as they contain carbon, the word part “hydro” as they contain hydrogen, and also contain oxygen represented by the -ate at the end of the word. Lipids, which can also be used as an energy source, are also made primarily of carbon, hydrogen, and oxygen. And proteins, which can be used for building materials among their many other functions, will contain a large proportion of carbon, hydrogen, and oxygen too.

However, there are many other elements and minerals that are essential for a healthy organism, and these may differ between different species. In plants, the essential nutrients required are divided into two main groups: macronutrients and micronutrients. Macronutrients are those that are needed in relatively large quantities. In fact, the prefix macro- actually means large or long. For instance, nitrogen is a key component of amino acids. Nitrogen can be absorbed from the soil and into the plant roots, where it can be used by the plant to produce the amino acids that will join together to make proteins. Proteins are one of the four major biological macromolecules in living organisms. Therefore, nitrogen is needed in considerable amounts.

If soil is deficient in nitrogen, the plant won’t be able to absorb as much as it’s needed, and the leaves will begin to turn yellow and the plant could potentially die. As we mentioned earlier, carbon, hydrogen, and oxygen are all essential components of almost all organic compounds in plants. So a lack of these elements will result in very poor growth as no carbohydrates, lipids, or even proteins will be able to be synthesized. This will cause wilting of a plant and eventual death.

Carbon alone makes up around 45 percent of the dry mass of a typical plant. Magnesium is a key component of chlorophyll, which is the main pigment found in the chloroplasts of most green plants that absorbs sunlight to provide the light energy needed for photosynthesis. As photosynthesis is the way a plant makes its food, magnesium must be absorbed from the soil in large quantities. Without magnesium, chlorophyll would not be synthesized. The leaves would turn yellow and photosynthesis would not take place.

In plants that usually produce flowers, a lack of available nutrients can also result in the prevention of the growth of these flowers. Some other nutrients that plants require in large quantities are phosphorus, potassium, calcium, and sulfur. Micronutrients are elements that are required in much smaller amounts, no more than a few milligrams per liter, and so can be referred to as trace elements. In fact, the prefix micro-, which you might’ve heard used in the word microscope or microscopic, means small.

Most micronutrients act as cofactors in enzymatic reactions. A cofactor is a nonprotein component of an enzyme that helps the enzyme to catalyze a specific reaction. As you can see when the cofactor binds to the enzyme, it allows the substrates to bind more easily. For instance, iron is a cofactor for proteins that are involved in important metabolic processes like cellular respiration and photosynthesis. Other micronutrients needed by plants often include manganese, zinc, boron, chlorine, copper, and molybdenum.

Some of the nutrients that need to be absorbed by a plant will be in the form of ions. Ions are electrically charged atoms or groups of atoms that forms an electrically charged molecule. Positively charged ions such as potassium, calcium, and magnesium are called cations. Negatively charged ions such as sulfate, nitrate, and chloride are called anions. A useful way to remember the difference between cations and anions could be that cats make you smile, so cations are positive. But onions can make us cry, so anions are negatively charged. If you’re not a fan of cats, you may have to think of another way to remember this distinction however.

Let’s take a look at how these cations and anions can be absorbed by the roots of the plant. This diagram shows a magnified view of a root hair cell, which are the specialized cells that make up a lot of the plant roots. The area surrounding the cell represents the soil, and these pink dots represent calcium cations in the soil. In the case of these calcium ions, you can see that their concentration is higher in the surrounding soil than it is in the root hair cell. When this is the case, these ions will move into the root hair cell by a process called diffusion. Diffusion is the movement of particles from an area of high concentration to an area of comparatively lower concentration.

Take a look at this diagram on the left and see which way you think the particles will move. If they’re moving by diffusion, they’ll move from left to right as the left side has a higher concentration of particles than the right side does. This will continue until each side has an approximately equal concentration of this particular ion. Diffusion is a passive process as it does not require an energy input from the organism itself. When particles move by diffusion, that’s sometimes described as going down or along their concentration gradient from an area of high concentration to an area of low concentration. A way to remember this could be that if you’re cycling down a hill, you do not need to input any energy. Instead, it’s a passive process, and you roll down the hill like the particles in diffusion move down their concentration gradient.

The cell wall of root hair cells tends to be relatively thin to allow the passage of substances like water and ions. It can also be described as permeable as it allows many substances through it. Beneath the cell wall is the cell surface membrane. This can be described as semipermeable as it allows certain ions to pass through it but prevents others from doing so if they are too large or charged, for example. However, we know that ions are charged. So how do they pass through the cell surface membrane? The cell membrane of root hair cells also demonstrates selective permeability. This means that it can select certain substances to allow into the cell based on the cell’s current needs. And there will be channels embedded in the cell surface membrane that allow these certain substances to pass through it.

Sometimes the concentration of ions in the root hair cell will be higher than that in the soil, for example, these potassium ions. These ions still need to move into the root hair cell, so they’ll be traveling from an area of low concentration to high concentration, which means they’ll be going up or against their concentration gradient. If we think back to our bicycle analogy, what do you think would be required if we’re going uphill? An uphill cycle, just like moving substances against or up their concentration gradient from a low to high concentration, is an active process. So it requires an input of energy from the organism itself. If you didn’t input energy, the bicycle would just start rolling back down the hill again.

As these potassium ions cannot diffuse into the cell, they will move into the cell against their concentration gradient by a process called active transport. This process describes the movement of particles across a plasma membrane from an area of their low concentration to an area of their high concentration using an input of energy. This energy is supplied in the form of a molecule called ATP, which is an energy-carrying molecule found in all living cells.

Let’s have a go at interpreting some experimental data on a graph that demonstrates active transport of minerals in a particular type of photosynthetic organism. The Nitella genus is composed of multiple species of green algae that grow in water, one individual of which we can see in this drawing on the right. In the graph on the left, we can see the concentration of chloride, potassium, magnesium, calcium, and sodium ions, both in the Nitella cells and in the surrounding water. For each ion, we can see that the concentration in the surrounding water is comparatively much lower than it is in the Nitella cells.

However, we know that all of these ions are essential to maintain a healthy and functioning organism. In fact, potassium, magnesium, and calcium are all macronutrients. So these especially should be being absorbed by the algae in relatively large amounts. If we take a closer look at one of the cells in the Nitella algae, we can see that magnesium ions, for example, which have not been drawn to scale, are in a lower concentration in the surrounding water than they are in the Nitella cell. Therefore, it’s not possible for these ions to diffuse into the root.

So what do you think will need to happen to allow these nutrients to be absorbed? Pause the video and see if you can work it out based on what we’ve learned so far. If you said active transport, good job. And if you said that it would require energy in the form of ATP to do this, even better. These ions will be actively transported using an input of energy supplied by ATP into the algal cells to keep the algae functioning correctly.

By looking back at the graph, we can see that these ions are also selectively absorbed. Remember, this refers to the plant taking in more of some ions than others depending on their nutritional need. For example, the Nitella algae is absorbing a higher volume of chloride ions than sodium ions. And the concentration gradient between the surrounding water and the Nitella cells is far steeper for chloride ions than it is for sodium ions, which generally means that more energy will need to be expended to transport these chloride ions into the cell than it would be for sodium.

Let’s see how much we can remember about absorption of minerals in plants by having a go at a couple of practice questions.

If there is a high concentration of potassium ions in the soil, they move to an area of low concentration in the roots. What term is given to this process? (A) Diffusion, (B) synthesis, (C) osmosis, (D) digestion, or (E) active transport.

Much like humans, plants need to obtain a certain amount of different nutrients to stay alive and healthy. Potassium is a crucial nutrient in plants as it plays an important role in biological processes like protein synthesis and photosynthesis. When particles or molecules are found in large concentrations in a particular area, they tend to spread out and move into areas where there’s a lower concentration of these particles or molecules. If this process is occurring over the surface of a membrane such as that in the root, the potassium ions will continue to move across this membrane from an area of high concentration to low concentration until eventually the concentration of molecules either side of the membrane evens out. This process is known as diffusion.

Diffusion is described as a passive process as it does not require energy to move the particles from an area of their high concentration to an area of their low concentration. In the question, we’re told that potassium is in a high concentration in the soil and moves to an area of lower concentration in the roots. So we know that the potassium ions will be moving into the roots where it’s in a lower concentration by diffusion.

Let’s try another question together to apply our knowledge and graphical skills.

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.

Now, let’s summarize what we’ve learned about absorbing minerals by reviewing the key points from this video. We’ve learned how all living things require some form of nutrition including mineral ions to function effectively. And when plants do not obtain the essential nutrients they require, they can become discolored, wilt, and even die. While macronutrients are those that plants require in comparatively large quantities, micronutrients are only required in smaller quantities. Finally, we learned that there are two main processes by which plants and algae absorb their nutrients passively via diffusion and actively via active transport.

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