Cell Structures

Alicia volunteered to become an organ and tissue donor when she got her state ID. If Alicia dies, she can help to improve others’ lives. Her heart tissue, skin, bones, and veins can all be transplanted into a patient in need. Choose the word that correctly completes the sentence.

A group of similar _________ make up a tissue.

• molecules

• cells

• organelles

• organ systems

Answer explanation

Stated correctly, a group of similar cells make up a tissue, and several tissues make up an organ. The levels of organization are atoms → molecules → cells → tissues → organs → organ systems → organism. Each level in this sequence grows more complex as the levels progress.

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Alicia volunteered to become an organ and tissue donor when she got her state ID. If Alicia dies, she can help to improve others’ lives. Her heart tissue, skin, bones, and veins can all be transplanted into a patient in need. Choose the word that correctly completes the sentence.

A group of similar cells make up a tissue. Several tissues make up an ________.

• organelle

• organism

• organ system

• organ

Answer explanation

Stated correctly, a group of similar cells make up a tissue, and several tissues make up an organ. The levels of organization are atoms → molecules → cells → tissues → organs → organ systems → organism. Each level in this sequence grows more complex as the levels progress.

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All the organelles in a cell work together to help the cell and the whole organism function. Some diseases are caused by the failure of one type of organelle. Read the description below of an example of this type of disease. Lauren has cystic fibrosis. Her body is unable to control the flow of salt into and out of her cells. Lauren’s symptoms include coughing and wheezing when she tries to exercise. She receives breathing treatments that let her swim, dance, and sing. Which organelle is affected by Lauren's disease?

• mitochondria

• cell membrane

• cytoplasm

• cell wall

Answer explanation

The correct answer is “cell membrane.” The cell membrane is the border between the cell and its environment. The cell membrane controls which substances enter and leave the cell. Animals, including humans, do not have a cell wall around their cells. Mitochondria convert the energy in food into cellular energy; they do not control which substances can leave or enter the cell. The cytoplasm circulates materials inside the cell.

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All the organelles in a cell work together to help the cell and the whole organism function. Some diseases are caused by the failure of one type of organelle. Read the description below of an example of this type of disease. Joe’s cells can’t convert food energy effectively into energy they can use. As a result, he gets extremely tired, has weak legs, and can’t breathe well. Joe swims every day to keep his body as strong as possible. Which organelle is affected by Joe's disease?

• nucleus

• mitochondrion

• cell wall

• chloroplast

Answer explanation

The correct answer is “mitochondrion.” The function of mitochondria is to convert food energy into energy that is usable for cell functions. Mitochondrial diseases result in too little energy for muscles and organs to function well. The nucleus contains DNA and controls the cell’s activities. Cell walls and chloroplasts are not found in human or other animal cells at all.

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All the organelles in a cell work together to help the cell and the whole organism function. Some diseases are caused by the failure of one type of organelle. Read the description below of an example of this type of disease. A mosaic is a picture made up of small colored pieces. Mosaic viruses cause plant leaves to look like mosaic art. A mixture of dark and light green patches appear on the leaves. The light green patches are not able to capture much energy from sunlight. Which organelle is affected by mosaic viruses?

• cell membrane

• mitochondrion

• chloroplast

• cell wall

Answer explanation

The correct answer is “chloroplast.” Chloroplasts are plant organelles that capture energy from sunlight and store it to use to make food. Healthy chloroplasts are typically bright green. Cell walls provide structure for plant cells. The cell membrane controls which substances can enter and leave the cell. Mitochondria convert energy stored in food to energy the cell can use to carry out its functions.

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Dr. Lopez studies the cells of oak trees that grow on steep hills. He is learning how the trees can support themselves and get enough food. The trees have very different needs than animals. Describe two structures found in plant cells but not in animal cells. How do these structures help plant cells to meet a plant’s needs?

Answer explanation

Animal and plant cells include many of the same structures. If you answered cell membrane, endoplasmic reticulum, nucleus, ribosomes, etc., these structures are found in both plant and animal cells. Vacuoles are also found in plant and animal cells, although they can be much larger in plant cells. Sample: Plant cells have a cell wall and chloroplasts. The cell wall protects and supports the cell. Chloroplasts take in energy from sunlight and use it to make food for the cell.

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Mad cow disease is caused by deformed proteins called prions. The disease is spread when meat from an infected cow is eaten. Prions can make normal proteins deform into more prions. After a few years, the brain of an infected person or cow looks like a sponge full of holes. Are prions considered organisms?

• Yes, because they can cause disease.

• Yes, because they can make more of themselves.

• No, because they are not made of cells.

• No, because they can't make their own food.

Answer explanation

The correct answer is C. All organisms are living things. All living things are composed of cells. Non-living things, such as viruses can cause disease, so A is not correct. The host of the non-living virus replicates it, so B is not correct. Animals, such as humans, cannot make their own food and are living things, so D is not correct.

The ghost plant is white with a single stalk. The ghost plant is a parasite that feeds on the roots of plants. The roots of a ghost plant join with the root-like structures of a fungi and trick fungi into obtaining food from the roots of trees under the ground.  Ghost plant cells have all the usual plant organelles, except the __________ are not needed to transform energy.

Answer explanation

The correct answer is chloroplasts. Since the ghost plants obtain food using fungi to decompose it for them, they have evolved to not need chloroplast to create food.

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A virus can reproduce only inside a cell. Once inside, the virus causes the cell to make many new copies of the virus. In an animal, which part of the cell is responsible for keeping viruses out?

• cell membrane

• nucleus

• vacuole

• cell wall

Answer explanation

The correct answer is A. The cell membrane is the outmost portion of the cell. It functions as a barrier to keep things out of the cell and allow things to enter the cell. The nucleus directs the cells activities, so B is not correct. The vacuole stores water, food, waste products, or other materials, so C is not correct. The cell wall protects and supports a plant cell and is not present in an animal cell, so D is not correct.

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Before a new medicine is approved, scientists study the effects the medicine has on different parts of the body. Often, a medicine is tested on mice before it is tested on humans. All the cells in the illustration below came from the same mouse.

If all of these cells are mouse cells, why do they look so different from each other?

• Cells change shape as they get older.

• Different cells specialize in different functions.

• Each kind of cell is from a different organ system.

• Different-shaped cells came from different ancestors.

Answer explanation

The correct answer is “Different cells specialize in different functions.” For example, nerve cells can be long and branched to make connections between several different cells. Red blood cells are flat and round to slip easily through narrow blood vessels. Each type of cell stays about the same shape throughout its life. The different organ systems contain many of the same types of specialized cells. Animals do not inherit cells from their ancestors – they inherit DNA.

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