Question Video: Recalling the Adaptations of Muscle Cells | Nagwa Question Video: Recalling the Adaptations of Muscle Cells | Nagwa

Question Video: Recalling the Adaptations of Muscle Cells Biology • First Year of Secondary School

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Muscle cells (also known as muscle fibers) are an example of specialized cells. Which of the following is correct about muscle cells? [A] Muscle cells are small spherical cells that contain large nuclei. [B] Muscle cells group together to form bundles that contract and relax to move the body. [C] Muscle cells do not contain a nucleus, which gives them more available space to carry oxygen. [D] Muscle cells are the largest cells of the human body.

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Video Transcript

Muscle cells, also known as muscle fibers, are an example of specialized cells. Which of the following is correct about muscle cells? (A) Muscle cells are small spherical cells that contain large nuclei. (B) Muscle cells group together to form bundles that contract and relax to move the body. (C) Muscle cells do not contain a nucleus, which gives them more available space to carry oxygen. Or (D) muscle cells are the largest cells of the human body.

This question is asking about how muscle cells are adapted to their function. To answer it, let’s recall the key facts about specialized cells, focusing in particular on muscle cells. All our cells start off as stem cells, which are simple and unspecialized. Stem cells can divide and form new cells, which can then differentiate to become specialized. This means they develop into cells which possess adaptations to allow them to carry out their specific job.

There are many, many different specialized cells in the human body. Examples include red blood cells, lymphocytes — cells of the immune system — egg cells, sperm cells, and muscle cells.

As you can see from this diagram, each has its own specific shape and specialized features. For example, mature red blood cells have no nucleus, so they can be packed full of hemoglobin to carry oxygen around the body. Lymphocytes are small spherical cells with a large nucleus to code for the antibodies they produce to defend against pathogens. Sperm and egg cells, the smallest and largest cells in the body respectively, have nuclei which only carry half the normal number of chromosomes. So when fertilization occurs and their nuclei fuse, the normal number is restored.

However, this question is specifically asking about muscle cells, so let’s look at how these are specialized for their role in the body.

Muscle cells, also known as myocytes — myo- meaning muscle and -cytes meaning cells — or muscle fibers, are specialized to bring about movement. There are three main different types of muscle cell: skeletal, cardiac, and smooth or involuntary.

Skeletal muscle is under voluntary control; in other words, we have conscious control over its contraction. It is attached to your bones and brings about body movement.

Cardiac muscle in the heart contracts rhythmically without tiring to pump blood around the body. It is under involuntary control, which means we do not have to think about it — obviously important when it has to contract constantly to keep us alive.

Smooth muscle, also under involuntary control, is found in many hollow internal organs such as the small intestine, arteries, and bladder. It is designed to contract slowly and persistently, unlike skeletal muscle which needs to contract and relax quickly.

Each type of muscle tissue has a different role to play within the body, but all of the roles involve contraction. The cells therefore have adaptations in common, which allow them to carry this out effectively.

First of all, they contain special contractile proteins, which can shorten and so generate force. This contraction requires lots of energy. So, secondly, all three types of cell contain many mitochondria for aerobic respiration. Thirdly, because glucose is the best respiratory substrate, muscle cells have their own store of glucose: glycogen. Glycogen is made up of lots of glucose molecules joined together in a large branched molecule which is insoluble and unreactive. So it just sits in the cell until more glucose is needed.

Now we have reviewed the key facts about specialized cells in general and muscle cells in more detail, let’s return to the question, which asks, “Which of the following is correct about muscle cells?” We have seen the picture of the lymphocyte with its large nucleus and the red blood cells which have no nucleus, so we can rule out (A) and (C). We also looked at the egg cell, the largest cell in the body, so we can rule out (D). This leaves us with the correct answer, which is (B). Muscle cells group together to form bundles that contract and relax to move the body.

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