Parent Primer: Life Science
It seems like life science should be simple, given that you live in the world and know the difference between an animal, vegetable, or mineral. But around 4th grade, when your child starts asking you what phylum a dolphin is in, you may find yourself floundering for the answer. Use this primer to refresh your memory on plant parts, ecosystem essentials, and all the other wonders of life so you can help your child's love of science flourish. To go even further with your science study, check out Everything You Need to Know About Science Homework, a great reference designed just for parents of budding scientists.
What Is Life?
Classifying Life
Animal Basics
Plant Basics
Ecology
One of the first science questions your child will learn to answer is, "Is it alive?" Some answers are easy: cats and dogs are alive, rocks and plastic bags are not. But what about a sponge or a virus? Your student will have to ask if something is a living thing — an organism — by seeing if it does the following six things:
- It takes in energy and gives off waste.
- It grows and develops.
- It can adjust to its environment.
- It can respond to its surroundings.
- It can reproduce.
- It is made up of cells.
All organisms can do these six things.
If something is living, it is also part of one of five groups, or kingdoms:
- Animalia (Animals): Many-celled creatures that cannot make their own food, but instead must consume other animals and plants for energy. Their cells do not have rigid walls. Includes mammals, birds, fish, amphibians, reptiles, mollusks, sponges, worms, insects, and spiders.
- Plantae (Plants): Many-celled organisms that make their own food through photosynthesis. Their cells have rigid walls with cellulose in them. Includes flowers, trees, moss, grass, and ferns.
- Fungi (Fungus): Organisms that do not have chlorophyll, but instead dissolve their food and then absorb it. Their cell walls contain chitin. Includes mushrooms, molds, rusts, and yeasts.
- Protista (Protists): Micro-organisms (mostly one-celled) that have cells with a nucleus. Includes algae, amoebas, paramecia, diatoms, and euglenas.
- Monera (Monerans): One-celled micro-organisms that do no have a nucleus. Most absorb their food. Includes bacteria and thousands of other kinds of micro-organisms.
Once an organism's kingdom has been determined, scientists continue to separate out living things into smaller and smaller groups. This method of classifying helps people see what one animal might have in common with another. For instance, a dog and a cat both belong to the class of mammals, but they diverge at the genus level: cats are felines while dogs are canines.
The system of classification, going from broadest to narrowest, is:
- Kingdom
- Phylum
- Subphylum
- Class
- Order
- Family
- Genus
- Species
Within the animal kingdom, the most vital classification your child will have to master is vertebrate versus invertebrate.
- Vertebrates have a backbone. Includes mammals, birds, reptiles, amphibians, and fish.
- Invertebrates have no backbone. The majority of animals are actually invertebrates. Some have an exoskeleton — a hard outer skin — that protects their bodies. Others have shells, and still others have no protection at all. Includes insects, shellfish, spiders, worms, and sponges.
Another distinction within the vertebrates is cold-blooded versus warm-blooded. A common misconception is that cold-blooded animals, such as snakes, have literally chilly blood coursing through their veins. In reality, the difference is:
- Cold-blooded animals' body temperature depends on the temperature of its environment. If a frog is sitting on a sunny rock, its body temperature rises, but if it is hiding at the bottom of a cold lake, its temperature will be very low. To warm up or cool down, a cold-blooded animal such as a fish, reptile, or amphibian has to change locations.
- Warm-blooded animals' body temperature stays relatively constant no matter what the temperature is like around it. Birds and mammals are the warm-blooded animals.
Another way your child may be asked to classify animals is by what and how they eat.
- Carnivores eat meat (other animals). Lions and dolphins are carnivores.
- Herbivores eat plants. Giraffes, elephants, horses, and blue whales are all herbivores.
- Omnivores eat both meat and plants. Humans are omnivores, as are bears and many rodents.
- Predators hunt other animals to eat. Eagles, alligators, and cheetahs are a few of the many predators.
- Scavengers eat animals that are already dead or the leftovers from predators' kills. Vultures and hyenas are the most famous scavengers.
A final way your child may be asked to categorize is by whether a creature is diurnal or nocturnal.
- Diurnal animals are awake and active during the day and sleep at night. Most animals, including monkeys, pigs, zebras, and songbirds, are diurnal.
- Nocturnal animals sleep during the day and are awake at night. Includes owls, possums, moths, and raccoons.
Plants are divided into two groups: ones that make seeds and ones that don't. Some examples of seed plants are grasses, roses, broccoli, and trees. Plants that don't make seeds include moss and ferns. All of the non-seed producing plants make spores.
Plant Parts
Each part of a plant has a function:
- The roots anchor the plant to the ground, absorb water, and store sugars and starch.
- The stems support the plant and serve as a path for food and water to travel. Xylem tissues take minerals and water up from the roots to the rest of the plant, while phloem tissues take food made by leaves to growing areas.
- The leaves make food through photosynthesis and the undersides of leaves let the plant release water — this is called transpiration.
In flowering plants, the flower's main purpose is to produce seeds. Most plants contain both a male part called a stamen, which is made up of an anther and a filament, and a female part called a carpel or pistil, which holds ovules (the plant "eggs"), a stigma, and a style.
Plant Reproduction
Seed plants reproduce when the pollen from the stamen enters an ovule and fertilizes it. Some seed plants can also grow just from plant parts and not from seeds. Potatoes and other tubers and bulbs can grow new plants from the "eyes" which turn into root shoots. Many grasses and weeds grow through runners and rhizomes. Stems that run along the ground are runners, while those underground are rhizomes. New plants can sprout from the tips of either. In other cases, plants can send up new shoots from their roots or even leaves.
Non-seed plants use spores to reproduce. Spores are actually tiny bits of plant life (including a sperm and egg) that are stored until they are ready, then sent out on the wind to start new life. For fertilization, just add enough water so the sperm can swim to the egg!
Photosynthesis, Respiration, & Transpiration
Photosynthesis is the process by which plants use the sun's energy to make sugar. A green pigment in plant leaves called chlorophyll absorbs sunlight, combines it with water from the soil and carbon dioxide from the air and turns it into sugar. Oxygen is released as a by-product of photosynthesis, giving us the air we breathe.
Respiration is the process through which plants grow and survive. The plant breaks down food by using oxygen to release its energy. Carbon dioxide and water are released during the process.
Transpiration is a plant's way of sweating. The water that is absorbed through the roots passes through the pores on the underside of leaves and evaporates.
Ecology is the study of the relationships between life and its environment. An ecosystem is any place where plants and animals live together and rely on each other in their natural surroundings or habitat. The largest ecosystem is the whole planet Earth, and is called the biosphere. Most ecosystems that scientists (and your young scientist) study are much smaller, such as ponds, coral reefs, mountaintops, or fields. Sometimes scientists look at regions that share the same basic temperature and rainfall, like deserts, rain forests, and tundra. Each of these areas is called a biome. For more on the characteristics on the different climates, see the Geography Primer.
Any group of animals, plants, or other type of life that are the same species in the same area is called a population. All of the populations that live together in an ecosystem make up its community. When your child looks at an ecosystem, he might be asked how removing a population, such as frogs, would affect the community of a swamp. He will also study food chains and natural cycles within ecosystems.
A food chain looks at how one piece of food might move through the community. For instance, a piece of grass is nibbled on by a mouse that then gets snatched up by a bird, which a wolf then catches and eats. When the wolf dies, bacteria, insects, worms, and fungi will break down the remains and cause it to decompose. Then plants (like grass) can use the nutrients left in the soil to grow. Food webs are food chains that connect at some point — for instance, if that bird had flown off to another area and gotten eaten by a cat instead, which in turn was eaten by another predator. Almost all food chains are part of a larger network of a food web.
There are three natural cycles your student will become familiar with:
- Water cycle - The sun drives the water cycle by heating water in lakes, rivers, oceans, and the soil, making it evaporate and turn into a gas. This water vapor rises into the atmosphere until gravity drags it down to earth again in the form of rain, snow, and dew. Most of the falling water returns right back to the ocean, but animals lap some up and some is absorbed by the soil where plants can drink it. The plants sweat out the water through transpiration, animals let out some water as waste, and when animals and plants decompose, their bodies release the water that makes up most of their mass.
- Nitrogen cycle - Take two atoms of oxygen and one of carbon and you've got carbon dioxide (CO2), which is essential for photosynthesis. During this process, plants use the carbon to make food and new plant cells. Meanwhile, they release the oxygen that all animals breathe and plants use for respiration. The animals and plants then exhale CO2, and they also produce the essential gas during decomposition. Carbon also goes into long-term storage in the form of fossil fuels, such as coal and oil.
- Oxygen and carbon cycle - Take two atoms of oxygen and one of carbon and you've got carbon dioxide (CO2), which is essential for photosynthesis. During this process, plants use the carbon to make food and new plant cells. Meanwhile, they release the oxygen that all animals breathe and plants use for respiration. The animals and plants then exhale CO2, and they also produce the essential gas during decomposition. Carbon also goes into long-term storage in the form of fossil fuels, such as coal and oil.
