Chapter 6

Biology

Biology is the study of life and living organisms, including humans, animals, plants, and other organisms such as fungi, bacteria, and algae. In particular, biology focuses on studying the growth of these living organisms, how they populate, and how they function in order to survive.

Plants are in every person’s landscape—in your backyard, in a nearby park, or simply planted alongside the roads. Bacteria and fungi populate the world around us, as well as the world within our bodies. Every living thing produces offspring to make sure their species continue on.

In this chapter, you and your child will explore some basic concepts in the biology of plants, fungi, and humans, such as some of the functions that enable them to survive and some characteristics they pass down from generation to generation. Through these explorations, biology will “come to life” in your living environment. In addition, you’ll learn about some of the exciting vocations in the biological sciences.

ACTIVITY: How Plants Make Food: Photosynthesis

Every living organism needs to eat. Some are picky eaters; others are not. Plants in general are among the least picky eaters. The presence of forests that are not maintained by anyone shows that those plants are not finicky about their nutritional needs.

Plants use a process called photosynthesis to make their own foods in the form of sugars. Photosynthesis is a chemical process that can only occur within the biological systems of living plants. In this chemical process, the plant stores the energy of sunlight inside sugar molecules it makes from water and carbon dioxide molecules. It takes six water molecules plus six carbon dioxide molecules (plus sunlight) to make one sugar molecule and six oxygen molecules. Plants make their own sugars using only sunlight, water, and carbon dioxide, which is present in the air humans and animals expel from their lungs when they exhale. Plants take human waste gas products (carbon dioxide) and use it to make their own food.

The amount of sunlight a plant is exposed to has an effect on how much “food” it can make for its own growth. There’s an easy way to observe how sunlight directly affects a plant’s ability to make food for itself so it can grow.

Materials Needed:

Procedure:

  1. It’s best to do this experiment during a warm season. Have your child make a thick layer of cotton wool in both plates, then slightly spray each with water to dampen the cotton.
  2. Now ask your child to sprinkle some of the mustard seeds on each of the cotton surfaces. Have her spray the seeds with water again until the cotton wool is lightly soaked with water and the seeds are wet on top.
  3. Have your child place one of the plates in a dark corner of the house that doesn’t get sunlight at all, and the other plate near a window that gets plenty of sunlight throughout the day without being in direct sunlight.
  4. Have your child check the moisture of the cotton wool in both plates every day. If she’s doing this experiment in the summer, she might want to spray the plate in the lit spot once in the morning and once in the evening to make sure the seeds don’t get dry.
  5. Have her check and see if her seeds are sprouting in the first ten days. Once they do, have her observe how fast those sprouts grow in the plate that gets sunlight compared to the one that doesn’t. Ask her if there’s a difference in the sprouting speed in both plates.
  6. Urge your child to look after her two plates and touch the cotton wool on each to check for dampness every day. In about 30 days there should be a full canopy of mustard greens on at least one of them. Which one has the full canopy of greens?
  7. Encourage your child to continue to spray both plates with water and to keep the cotton wool damp on each for another ten to fifteen days. Which plate has its mustard greens grow taller?

If your child reports back to you that the mustard greens in the plate near the window that gets sunlight experienced the fastest growth, she now understands how critical sunlight is to the plants’ growth.

STEM Career Choices

Botanist

Botanists are plant scientists. They study the plants’ organisms as well as their interaction with their surrounding environment. They may also conduct experiments on plants to investigate how they grow and survive under different conditions.

A botanist may be concerned with studying the large, naked-eye characteristics of plants, or may be interested in looking through microscopes at the plants’ cellular level. Botanists may also be interested in studying processes that take place on the molecular level, such as photosynthesis. They may be interested in conservation, such as focusing on conserving native plant species against the invasion of non-native plants.

Everything grows when it eats and gets nutrients. The way plants make food for themselves using sunlight, water, and carbon dioxide through the photosynthesis process involves something in their green leaves called chlorophyll. The molecules of chlorophyll are found in every green plant, and it’s what makes plants and algae look green. These molecules absorb sunlight and use the energy that reaches them from the sun to make (or synthesize) sugars from basic ingredients like water and carbon dioxide. This entire process the chlorophyll molecules perform is what’s called photosynthesis. The chlorophyll molecules can synthesize sugars (food for the plant) by using sunlight. That’s where the name photo (meaning light) and synthesis (indicating that it is making something) comes from.

All the energy in the sunlight absorbed by the plant is stored inside the sugar for later use. One interesting result from photosynthesis is that plants release the oxygen freed through the process back into the air. As the plant uses carbon dioxide and water coupled with sunlight, it not only makes sugar inside its own “body” but also releases oxygen as a result of that process. This is why there’s a concern about losing more trees and forests on Earth. The plants “breathe out” oxygen for humans and animals to survive, so a reduction in that oxygen source is cause for concern.

STEM Career Choices

Ecologist

Ecology is a science that is concerned with the relationship between living organisms such as plants and animals and the environments in which they live. Ecologists specialize in certain types of environments. For example, marine ecologists work with plants and animals that live in seas and oceans.

Ecologists may study environmental pollutants that affect the life and reproduction of living organisms. They also study the consequences of human activities on the environment. They may be found working at sites where pollution is taking place—for example, at chemical and oil spills in rivers and seas.

ACTIVITY: Deciduous versus Evergreen Trees

Depending on where you live, you may see trees that lose their leaves for part of the year and become “naked,” trees that keep their leaves yearlong, or a combination of both. This behavior in a tree is part of the tree’s scheme to survive in the environment in which it lives.

In general, trees are categorized in two ways with respect to whether they lose or keep their leaves throughout the year: deciduous and evergreen trees. Deciduous trees lose all their leaves during certain parts of the year, while evergreen trees keep their leaf coverage year round. Most trees with needle-leaves, which are members of a family of trees known as coniferous trees, are evergreen trees.

STEM Q&A

Q: Are there other deciduous plants besides trees?

A: Yes. Any plants that lose their leaves during certain parts of the year are called deciduous. This includes shrubs and herbaceous perennial plants that live for several years. Examples include mint and basil as herbaceous plants, while lavender and Russian sage are considered shrubby perennials.

Your child would learn a great deal about the natural world in his immediate environment by creating an inventory of the trees in your area. With a few specific observational tools he might grow fond of studying trees and plants.

Materials Needed:

Procedure:

  1. This is an activity that may span the length of two seasons starting with summer. Take a walk with your child with the intent to study the trees in your neighborhood. Help him become familiarized with the different shapes of the mature trees on the first walk. Tell him to notice the shapes of the trees. Are they round or cone-shaped, or some other shape? Remind him to record his observations in his notebook at the end of the walk. You might want to encourage him to draw a sketch or take a photo of each tree so he can remember them later.
  2. The second time you go for a walk, ask him to notice the shapes of the leaves on the different trees he identified the first time. Ask him to specifically notice if the surfaces of the leaves are wide and big, or narrow and small. You can prompt him to collect a leaf sample if the tree is near the sidewalk. Remind him to record these additional observations in his notebook when he’s done. Encourage him to sketch the outline of each leaf. This will help him assess how large or small the leaf size is.
  3. As the days progress, help him become aware of which trees lose their leaves and which ones stay green. Remind him to record his observations in his notebook.
  4. Do the same activities when you have a chance to visit a nearby park. In a park environment, your child has opportunities to observe more trees, and to collect more leaf samples for his sketches.

At the end of the fall season, you can go through your child’s notebook with him to examine what information he has collected. You can help him organize his findings by asking him a few simple questions: How does the size of the leaves from trees that shed their leaves compare to those leaves from trees that didn’t? In other words, was the leaf size of deciduous trees significantly different than the leaves of evergreen trees? Which ones were larger? Also, how did the shape of a deciduous tree compare to that of a evergreen tree? Encourage your child to look back through his notebook for answers to these questions.

If your child noticed that deciduous trees have leaves that are large in surface area compared to evergreen trees, then he’s figured out one important clue to identifying which trees are deciduous or evergreen. Also, if he noticed that deciduous trees have a rounded shape on top, he now has two clues. Here’s where you can assist him in putting it all together so he can see the bigger picture.

STEM Career Choices

Environmental Scientists and Environmental Engineers

Environmental scientists use their skills and knowledge in science to protect the environment, along with the health of human beings. They’re often involved in the cleanup of polluted areas. They also play an important role in advising policymakers in creating new policies pertaining to the environment.

Many environmental engineers are employed in industry to help reduce pollutants and waste. When working in the field, they collect samples in order to analyze them in the laboratory. This allows them to make recommendations on reducing hazardous material produced during industrial processes.

Deciduous trees require more nutrients in order to grow and survive. They do so by first growing broad leaves that can take in more sunlight. That’s why their leaves are relatively larger than those of evergreen trees. The large leaves increase their photosynthetic abilities. They also maximize the amount of sunlight each leaf receives by having a round canopy on top. The roundness of the canopy allows more leaves to be exposed to sunlight. When the trees eventually shed their leaves and the leaves fall on top of their roots, the leaves break down and compost over time, enriching the soil with nutrients for the next growing season. These trees essentially produce their own fertilizer.

Such trees can’t survive in an environment that’s very harsh, where the soil is poor and water is scarce.

Evergreen trees work differently. Their leaves are very small compared to the leaves of deciduous trees. Their leaves can look needle-like, and aren’t exposed to as much sunlight as the broader leaves of deciduous trees. This isn’t a problem for evergreen trees because they keep their leaves year round, and so photosynthesis happens throughout the year. The needles on an evergreen tree don’t all fall at one time because such trees don’t need soils that are rich in nutrients. Evergreen trees don’t require fertilizer in the way deciduous trees do; they’re fine making just enough food from photosynthesis year round using their tiny leaves. Some evergreen trees’ conical shape helps minimize damage by wind, ice, and snow.

STEM Career Choices

Marine Biologist

Marine biologists study all kinds of creatures that live in the seas and oceans. This includes fish such as sharks (for fishery biologists), mammals such as whales and dolphins (for marine mammalogists), and microscopic organisms such as plankton (for microbiologists).

Marine biologists are often engaged in research as well as education. This means they work in or with educational institutions such as universities, and also zoos and aquariums. They may also work on a body of water in which aquatic creatures live to ensure environmental standards free of pollutants. Marine biologists are employed by both the public and private sectors, and by both for-profit and nonprofit employers.

There are more deciduous trees and forests in the eastern half of the country, where water is abundant and the soil is richer with nutrients. More evergreen trees are seen in the western half of the country, where the climate tends to be harsher and the soil poorer in quality. Examples of deciduous trees are oak, maple, mulberry, black walnut, birch, and elm. Some examples of evergreen trees include pine, firs, spruce, and junipers.

ACTIVITY: Fermentation: Making Sourdough Starter

Bread has been an essential staple for human beings for thousands of years. The most commonly consumed bread today relies on a very important biological process called fermentation. Fermentation is a chemical process that involves microorganisms such as yeast or bacteria. The fermentation process converts sugars and carbohydrates into alcohol, releasing carbon dioxide gas.

Fermentation doesn’t only occur during the process of making bread; other examples of fermentation happen during the process of making wine and beer. Fermentation is also occurring when milk becomes yogurt.

STEM Career Choices

Microbiologist

Microbiologists study microorganisms, including bacteria, algae, fungi, viruses, and parasites. This is a world too small to be observed with the naked eye, so microbiologists use microscopes to do their work. They investigate how these organisms multiply and how they interact with their environment.

Microbiologists often work in teams of researchers. Their investigations include not only the harmful effects of some of these microorganisms, such as viruses, but also their important functions that are essential to life, such as some bacteria, fungi, and algae. Microbiologists are found working in hospitals and medical schools. They also work in government laboratories and in industry.

Is it possible to observe the process of fermentation? When bread rises as the dough sits in a warm place, it seems difficult to notice fermentation happening. There is the before-and-after effect, where the dough seems to have doubled in size. But is there a more direct way to “see” the fermentation process release carbon dioxide gas?

Materials Needed:

Procedure:

  1. It’s best to do this experiment in a warm season. Have your child place 5 tablespoons of all-purpose, unbleached wheat flour in the glass jar.
  2. Now tell her to stir just enough spring water into the flour to make it the same consistency as pancake batter. Ask her to add the water gradually, stirring it into the flour. Assist her in gauging whether the consistency is like pancake batter, or if more water is needed. If the mix turns out too watery, tell her she can add a little more flour to fix it.
  3. Help your child to cut a piece of the cheesecloth to cover the top of the jar with some excess extending past the rim of the jar. You might want to tell your child that the cloth is used to cover the jar instead of a jar lid in order to allow the mix to “breathe.”
  4. Now have your child secure the cheesecloth around the rim of the jar with a wide rubber band. Have her place the jar in a warm room, but not in direct sunlight.
  5. Inform your child that she’ll need to stir the mixture with a spoon once a day for several days in order to prevent mold from forming on the surface.
  6. After about two days (depending on the temperature of the room in which the jar sits) have your child look closely at the contents of the jar. What does she observe? Are bubbles beginning to form?
  7. Encourage your child to check on her jar every day and observe the changes happening inside of it. Are there even more bubbles forming every day?
  8. When the bubbles start to make the batter rise in the jar, let your child know that it’s time to “feed” those microorganisms inside the mix with a few more tablespoons of flour. Remind your child to also add a little more spring water. Tell her to add just enough water to keep the mix at the consistency of pancake batter.
  9. Now have your child observe the contents of the jar closely, perhaps two or three times a day, in order to see the changes that will happen more quickly. Look for more bubbles in the mix. Ask your child if she observes how those bubbles make the mix rise inside the jar. When this happens, the starter mix is now ready to be used to make bread. A mix like this is called a sourdough starter.

This fermentation process is the ancient process people used to make bread for thousands of years. The reason the flour starts to undergo fermentation is because yeast is everywhere. This is the naturally occurring yeast that is present in the flour, in the air, on the skins of grapes and other fruits, etc. When the conditions are right—meaning when there is moisture and a warm environment, as well as “food” for the yeast in the form of sugars or carbohydrates—the yeast microorganisms start to “eat” those sugars and carbs, converting them into alcohol and carbon dioxide. It’s the carbon dioxide gas that shows up as bubbles in the starter mix, making it rise. It’s the active life cycle of those microorganisms that gives bread the ability to rise in order to have just the right texture.

As long as you continue to “feed” the starter mix by adding more flour and water, it will survive. There are families who’ve kept their sourdough starter “alive” for hundreds of years, passing it down from generation to generation.

Every time you need to make sourdough bread, you can use part of the starter to make the bread rise, then “feed” what remains in the jar with 2–3 tablespoons of flour and some water to bring it back to the same consistency as it was before. You can look up recipes online for sourdough bread.

STEM Career Choices

Biotechnologist

Biotechnologists work in a field that combines living organisms with technological application in order to make new products. Examples include designing organisms that can produce useful chemicals, such as antibiotics.

There’s a wide range of vocations available for biotechnologists. They include the fields of medicine and agriculture, among others. Some biotechnologists may work on environmental applications. For example, a biotechnologist may work on developing microorganisms to treat polluted water, or may produce plastics that are biodegradable in order to preserve the environment.

ACTIVITY: Potato, Carrot, and Cell Osmosis

When you feel thirsty, you reach for a glass of fresh water. Because the human body is composed of 70 percent water, this liquid is very important in many functions of the body, down to the level of the cells. But how do the cells “drink” water once the water is made available around the cells? The answer lies in something called osmosis.

Osmosis is a natural, biological process that happens whenever there are two water-based liquids with different concentrations present on either side of a surface that is semipermeable. For example, when there’s water with low salt content on one side of a semipermeable surface and highly salted water on the other side, some of the water from the low-salt side migrates and moves through the semipermeable surface into the high-salt side, until the concentration of salt on both sides becomes equal. It is specifically and only the water molecules that move from the low-salt side to the high-salt side in order for both solutions to reach equilibrium in salt content.

STEM Words to Know

semipermeable

A semipermeable surface is one that allows certain substances to pass through but not others. For example, plastic wrap is not permeable at all, while a cotton cloth is totally permeable, letting all liquids pass through. A biological semipermeable surface is a cell wall or membrane. It allows water (but not anything dissolved in the water) to pass through its surface.

In general, whenever something is dissolved in water, like salt or sugar, the dissolved substance is referred to as the solute, while the water is referred to as the solvent. Because water has a smaller molecule than the salt or sugar, the water molecules are the ones that move across the partially permeable (or semipermeable) surface.

But how does this work for cells of living things? Can the effects of osmosis be observed directly?

Materials Needed:

Procedure:

  1. Assist your child in peeling the potato.
  2. Use the apple corer to carve out a cylindrical piece of potato about 4" in length. This will take some effort, so you might want to assist your child in this process.
  3. Have your child tie a piece of cotton string around the potato cylinder with a double knot, then slide it off the potato cylinder. Have your child save that loop of string to use for measuring the diameter of the potato cylinder later.
  4. Fill one of the glasses with plain water and place the potato cylinder in the glass. You will be letting this piece sit in the glass for a few hours.
  5. Now have your child use the other glass to prepare a very salty water solution. Ask her to fill the other glass with water, then have her add 2–3 tablespoons of salt to the water. Stir the salt until it is all dissolved in the water.
  6. Have your child peel the carrot. After that’s done, tell your child to tie the other color cotton string around the widest part of the carrot with a double knot, then slide it off. Save that loop of string to use for measuring the diameter of the carrot later.
  7. Now tell your child to place the carrot inside the second, salty glass of water with the wide side of the carrot on the bottom (for stability). Allow the carrot to sit in the salty water for a few hours as well.
  8. A few hours later, have your child check on the potato cylinder. What has changed about it? Has it become fatter or more slender? Remind your child that she can use the string she tied around the potato cylinder earlier to measure. Does that tied string still fit around the potato cylinder after it has soaked in water?
  9. Have your child check on the carrot a few hours later as well. What has changed about the carrot? Is it still crisp and hard, or has it wilted and become somewhat soft? Has it become fatter or more slender? Remind your child that she can use the string she tied around the carrot earlier to measure. Does that tied string still fit snugly around the widest part of the carrot after it has soaked in salty water?

If your child found that the potato had increased in diameter, then she has visibly seen the effects of osmosis on the cells of that potato. Additionally, if she found that the carrot became wilted and more slender and that the string now fits loosely, then she’s seen the effects of osmosis on the carrot. Osmosis in the potato allowed water to move into the cells of the potato, and the potato became fatter. In the carrot, however, water moved out of the carrot cells and the carrot became thinner.

Imagine the wall of each cell inside the potato and carrot as a semipermeable membrane. On either side of the cell wall there is water (solvent). There are also many different substances that are dissolved in the water (solutes) inside the cell.

STEM Career Choices

Zoologist

A zoologist loves to study everything about animals. They’re passionate about the well-being of animals and like to educate the public about them. They identify certain animal species, document them, and observe these animals in the wild as well as in captivity.

Zoologists can also perform a wide range of jobs. They develop new veterinary medicines and test them. They work on identifying endangered species and habitats, and then conserving them. They do field as well as laboratory research. Zoologists also work in government agencies, as they develop new policies and regulations regarding wildlife.

When the concentration of the solutes inside the cell is high compared to the outside of the cell, water molecules move across the cell wall into the cell until the concentration of solutes is the same on both sides of that wall. This is why the potato cells inflate as water crosses the semipermeable wall into each cell. There’s a higher solute concentration inside the cells than outside, and water moves from the low to the high solute concentration until there’s equal concentration on either side of the cell membrane. This is how the cell “drinks.”

9781507200643 potato1

When the concentration of the solutes outside the cell is high compared to the inside of the cell, water molecules move across the cell wall out of the cell until the concentration of solutes is the same on both sides. This is why the carrot cells deflate as water crosses the semipermeable wall out of each cell. There’s a higher solute concentration outside the cells than inside, and water moves from the low to the high solute concentration until there’s equal concentration on either side of the cell membrane. This is how cells lose water.

This same process takes place inside the human body. Osmosis allows water to move into the cells or out of them. In order for cells to “drink” water, there has to be a lower concentration of solutes (or higher concentration of water) outside the cells for water to move into the cells. This is partially why water is so important for all living organisms. So the next time you drink water, remember that your cells are also drinking that water.

ACTIVITY: Dominant versus Recessive Traits

It’s often easy to identify which children belong to which parents at a school or daycare center. There are certain characteristics the children have that they’ve inherited from their parents. The parents’ genes determine the children’s genetics. Genetics is the study of hereditary traits, the differences and resemblances that get passed down from generation to generation in all living beings, humans, animals, plants, etc.

Genes are like a blueprint that carries instructions on how the child will look, among many other traits. Every child carries two sets of genes: one from the mother and one from the father.

Certain traits are determined by the set of genes one has inherited from both parents. One way traits can be categorized is by whether they are dominant or recessive. Dominant traits have a higher probability of expressing themselves than recessive ones.

There’s an easy way to observe recessive traits in people around you.

Materials Needed:

Procedure:

  1. Have your child look at all of his family members’ eyes and record the colors of each person’s eyes. Have him divide eye color into two categories: brown and blue (green eyes can be placed in the same category as blue for simplicity).
  2. If your own family members all have the same color eyes (all brown or all blue), then tell your child to look for a family that has mixed color eyes (perhaps the family of a school friend). Have him check the eye color of each member of that family and record his observations in his notebook.
  3. Have your child record his observations for some other families that are known to him.

Now it’s time for your child to examine his observations. Did he find one family where one parent had brown eyes while the other had blue eyes, yet all the children had brown eyes? If so, then he found the mostly dominant trait for eye color. Brown is the mostly dominant color of eyes. If one parent has entirely brown-eye genes, then most likely all the children of that parent will have brown eyes.

STEM Q&A

Q: Who is the father of genetics?

A: Gregor Johann Mendel lived in the nineteenth century, and is known as the father of genetics. He was from a region known today as the Czech Republic. His experiments on pea plants enabled him to understand how certain traits were inherited, establishing the rules of heredity. He coined the terms “dominant” and “recessive” to describe certain traits.

If the parent with brown eyes carried the genes for blue eyes, the blue-eye trait would not necessarily show up in that parent. But if that parent mates with another parent who has blue eyes, then the blue-eye genes have a higher chance of showing up in the children. When blue-eye genes from both parents show up together, then the child can have blue eyes. In other words, the parent with brown eyes can possibly carry the genes that can participate in the making of blue eyes in the children.

If the entire family has blue eyes in several generations, most likely all members of the family have only blue-eye genes. It would be very rare for anyone in that family to have brown eyes.

STEM Career Choices

Geneticist

Geneticists study genes. Genetics deals with traits that get passed down from one generation to the next. They may help shed light on a person’s health based on family history in terms of hereditary diseases.

Many jobs for a geneticist are in the medical fields and clinical research. Geneticists perform tests and interpret their results, often to individuals and their family members for whom the tests were made. Geneticists may work in other sectors such as law and public policy, as well as education. They may also work in the private sector with biotechnology companies.