Exchanging Materials: Specialized Cells, Tissues & Organs

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson we'll be looking at ways that plants and animals transport materials through their surfaces. We'll look at general characteristics of these types of tissues as well as specific examples such as the small intestine, lungs, gills, roots and leaves.

Why Do Living Things Exchange Materials?

Take a deep breath in. Now hold your breath for a few seconds. We start to feel uncomfortable quickly when we don't inhale and exhale routinely. Why is this? We inhale to get oxygen to our tissues to make energy and exhale to get rid of carbon dioxide, a waste product that is toxic to our body. When you hold your breath you start to feel uncomfortable because your body must continue this exchange to stay alive.

Breathing in and out is one example of how living things exchange materials with the environment. All living things are dynamic and must take in materials from the environment we need to stay alive and get rid of materials that are toxic to us. Today, we're going to look at some general characteristics of the tissues that exchange materials between the organism and the environment and then some specific examples in both plants and animals.

1. Large Surface Area

Materials that are exchanged in body need to move from one side of a surface to another. Imagine a crowd of people waiting to get into a concert. How long would it take them to get inside if there was only a single file line through one door? Now, imagine the same situation, but with large garage doors as the entry way. More people could get inside much faster.

The body wants to move materials as quickly and efficiently as possible, so many tissues and organs that exchange materials have a large surface area to volume ratio, meaning that the lining of the area is much larger than the space it contains. This means that more materials can be exchanged, thus making the tissue more efficient at doing its job.

Example: Small Intestine

The small intestine absorbs nutrients in animal digestive system. It's lining is folded upon itself in small structures called microvilli. These projections increase the surface area of the small intestine by up to 120 times greater than what it would be if the lining was smooth. This allows for efficient absorption of nutrients.

Microvilli increase the surface area of the intestine

Example: Root Hairs

Plants also need nutrients, just like we do. Although they make their own sugar, they still need minerals from the soil that are absorbed through the roots. Roots have specialized structures called root hairs that have long protrusions from their cell wall to increase surface area. This increases water and mineral uptake from the soil.

2. Thin Membrane

Exchange of many materials in the body happens through diffusion, where materials move from a higher concentration to a lower concentration. There needs to be a thin barrier between where the material starts and where it needs to end up for the process to be efficient. Many tissues that exchange materials have linings that are only one cell layer thick.

Example: Leaves

Have you ever picked up a pile of leaves? They're light and thin for a reason. Leaves are the organs that exchange gases with the environment for plants, similar to the job our lungs do. In order to do that they must be thin, providing an easy path for gases to get to the tissues they need to service. Gases move in and out of leaves through pores called stomata. The stomata open the atmosphere to the inner spongy area of the leaf, allowing for gas exchange.

3. Efficient Blood Supply

In multicellular organisms nutrients not only need to be exchanged with the environment, but also distributed throughout the body. This is accomplished through a closed blood supply that shuttles materials around the body. Tissues that are involved in material exchange are usually highly vascularized and have an extensive connection with the blood supply.

Example: Gills

If you've ever caught a fish, you might be familiar with their slippery scales, usually appearing in a shade of silver or blue. But, if you look near the head you can see bright red gills underneath their exterior. Gills are the gas exchange organs of fish. They are covered in tiny blood vessels called capillaries, which are why the gills appear red. Water washes over the gills in the opposite direction of the blood flow, allowing for efficient diffusion of oxygen into the blood. The blood then transports oxygen to the rest of the fish.

fish gills

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