Growth and Changes in Plants Unit Grade 3

Growth and Changes in Plants Unit – Grade 3

Contributions made by:

Trina Byrne

Serene Dittenhoffer

Denise Sullivan

Julie Titus

Lisa Whiting

Background Information for the unit on Growth and Changes in Plants

Seeds

Human babies grow protected and fed inside their mother’s bodies for nine months. Baby plants are sent off by their parent plants long before they are ready to start growing on their own. How can they survive alone? It’s all done with seeds. You’ve probably seen a fruit or vegetable with a seed inside of it. A tomato for example has many seeds whereas a peach contains only one. A seed is a tiny case containing plant life. It contains a small plant and food. Seeds come in all sorts of different sizes and shapes, but when a seed case is opened each contains a tiny plant called an embryo. The seeds contain food to sustain the tiny plant until it can make its own. The food storage is called the cotyledon. They are the leaves that are attached to the little plant or embryo. Some plants such as a bean have two cotyledons. Others, such as corn, have only one cotyledon. The hard outer coat of the seed protects the baby plant on its travels. When the seed begins to grow, one part of the embryo becomes the root and the rest becomes the upper stem and leaves.

Nearly all trees, shrubs, vegetables, and flowers started as seeds. Some of the seeds grow into seedlings and then into adult plants. Very few seeds actually survive, so plants produce an enormous number of seeds to insure reproduction of the plant.

Before a seed can sprout into a new plant, it has to land on the ground. Plants also need a lot of room to grow because if the new plant is too close to its parent they will have to fight each other for food and water. So, plants have invented lots of ways to spread their seeds. All seeds are remarkable in the way in which they spread themselves in order to grow new plants. Some seeds simply fall to the ground, others float on water, some are fired over a distance and others, like burrs, attach to animal’s fur. Maple seeds for example look like spinning helicopter blades. Dandelion seeds and milkweed seeds are attached to silky white tufts that act like parachutes. Other plants depend on animals to deliver their seeds for them. You’ve probably seen squirrels burying seeds and nuts. Well, they won’t find everything they’ve hidden so these uneaten nuts and seeds can grow into new plants. When birds and animals eat fruit, the hard seeds pass right through their bodies without being harmed and they come out in their droppings – far from the parent plant and fertilized too!

After a seed falls to the ground, it may sleep for some time. Many stay asleep for the winter. Seeds start to grow when conditions are right to support the needs of growing plants. In spring a seed starts to grow or germinate when it has water, warmth, and air. Water enters the seed and makes it swell and softens the seed coat. Inside the seed, the little embryo begins to grow and use its food supply. The hard outer coat cracks and the first little root pushes its way out. This root begins to take in more water and minerals from the soil. A root appears first and grows downward. Then a stem pushes upward towards the light. When it sprouts its first green leaves, the plant can begin to make its own food in its leaves. A new plant has begun its life.

Seeds are made in the fertilized ovule of a flower. Once a flower has been pollinated, seeds begin to develop. The part of the flower that holds the seeds starts to grow bigger. This part becomes the fruit, the protective structure surrounding the seeds. Plant species survive because of the seeds the fruit protects.

There are many kinds of seeds that we eat. Perhaps the most important plants in the world are grasses. Wheat, oats, corn, and rice are different kinds of grasses called cereals. The seeds of these cereals provide food for many of the animals we eat.

All seeds serve the same purpose, to germinate and grow a new plant in order to perpetuate the plant species.

Germination

Germination is the growing of a seed. Seeds start to grow when conditions are right to support the needs of growing plants. Water, oxygen and proper temperature are all necessary for seed growth. The stages from the swelling of the seed to the emergence of the first leaves are known as germination. A seed contains food to support the life of the tiny plant. When a seed begins to grow, it takes in water and swells. Usually the root tip emerges out of the seed first. This helps the plant absorb water and anchors the developing seedling. Next, the young stem and leaves emerge from the seed. The leaves turn green when sunlight reaches them and they start to produce their own food by photosynthesis.

Plant Growth

Flowering plants grow from seeds. A sprouting seed must absorb water before it will start to grow. It must have soil firmly packed around it and warmth from the sun. Inside the seed is a tiny embryo, surrounded by stored food. When the embryo starts growing, roots grow downward and a stem grows upward. There are growth hormones in plants that respond to the Earth’s gravitational pull and make roots grow down and stems grow up. This response is called geotropism (Greek for “turning to earth). Once the stem breaks through the surface of the soil into the sunlight, the first two true leaves form and the plant begins to make food. When plants have water, sunlight and proper minerals in the soil, they grow, manufacture food and give off oxygen.

Green plants produce food and oxygen from water, carbon dioxide and minerals through a process called photosynthesis. They take in carbon dioxide from the air, water and minerals from the soil, and energy from the sunlight. During photosynthesis, carbon dioxide and water are united in the presence of chlorophyll to form sugar and oxygen. The plant uses some of the food produced by a green plant as it grows and produces leaves and fruit. The remaining food is converted to starch and stored in the plant.

Plant Needs

Plants are organisms that grow and reproduce their own kind. They need food, air, water, light and space to grow.

Plants need soil. Water and minerals are taken from the soil through roots. Soil also provides support for the plant and an anchor for the roots to grow in. Decaying plants and animals leave behind minerals in the soil that are essential for future plant growth.

Plants need sunlight in order to grow properly. They use light energy to change the materials – carbon dioxide and water into food substances (sugars). This process of food production is called photosynthesis. Only in light can a green plant make food.

Plants must also have clean air. Green plants take in carbon dioxide from air and use it during photosynthesis to make food. Dirty, smoggy air blocks sunlight that plants must have.

Plants need water. Water is essential to all life on earth. No known organism can exist without water. Plants use water to carry moisture and nutrients from the roots to the leaves and food from the leaves back down to the roots.

Plants must also have space in order to grow. Plants are found everywhere – deserts, mountains, arctic regions, forests and jungles, oceans and even in cracks of sidewalks of busy cities. If the space is small, the plants will be small and stunted. Big plants need big spaces for their roots and branches.

Soil

Soils provide the water and minerals that a plant needs. Without soil, the plant can be watered, but it becomes difficult to give the plant the nutrients that it gains from the soil. Soil also provides support for the plant and its root system.

Soil usually has three separate layers. The top layer contains minerals and humus, the decayed remains of animals and plants. Plants for good growth need humus and minerals. The second layer contains humus and minerals that have been leeched from the topsoil. The third layer consists of rocks that are being broken down to form soil.

A great aid to the enrichment of soil is the earthworm. Earthworms burrow through the soil and leave castings of digested leaves and other matter, which help enrich the soil. They also improve the soil with their tunnelling by making it easier for air and water to soak in. Earthworms do not make poor soil into good soil, but rather they keep the soil in good condition for growing.

Water

Water is perhaps the most important substance to life on earth. No known organism can exist without water.

Plants, like every other living thing, need water in order to live and grow. Water carries the dissolved minerals and nutrients from the soil to the plant and carries food from leaves back down to the roots.

The plants get water in several ways – through rainfall, irrigation and dew. In our homes we water our plants. Most plants get water from rain. Even in the desert areas plants would die without moisture.

Sunlight

Plants need food and can make their own food. But they need things from which to make their food. Green plants need carbon dioxide from the air, water and minerals from the soil, and energy from the sun.

Only in light can a green plant make food. The process of food production is called photosynthesis. In photosynthesis, the carbon dioxide and water are changed to carbohydrates and oxygen. Food can only be made in the presence of chlorophyll. Chlorophyll is the substance responsible for a plant’s green colour.

When a green plant is deprived of sunlight, it soon loses its chlorophyll. It cannot make food, so it dies.

Space

Plants are found everywhere – gardens, lawns, forests, flower pots, hillsides, or in the water. Plants can even be found in cracks in the sidewalk and cracks in tar. If the spaces are large, the plants tend to be large. Plants can grow up, down, around a tree, across the soil, in the water and almost all kinds of places.

Temperature

Different kinds of plants live in different places. The temperature, length of season and amount of rainfall helps to determine the kinds of plants that will grow in a place.

Proper conditions for plant growth can be created on farms and in greenhouses.

Plants can be found in deserts where it is hot and dry. They grow in the forest and in grassland areas. Type of soil, amount of water, sunlight and temperature help determine what kinds of plants live in any one place.

Bulbs

Bulbs are a special type of plant. Unlike seeds, bulbs do not need soil because they carry their own food supply. Seeds require soil to grow because they need the nutrients (vitamins) from the soil. Bulbs consist of a round, underground structure that develops in some plants. The bulb is made up of thickened layers of fleshy leaves, which hold the stored food. In the centre is a large bud scale that produces the new plant. Roots grow from the solid basal plate. The outer scales from a dry and papery covering.

The purpose of the bulb is to store food. When the pant is growing, it stores food in these fleshy underground leaves. When the winter comes the above ground plant dies, but the bulb with its stored food remains alive underground. When the new growing season begins, the bulb’s central bud sends out a shoot, which produces a stem, leaves and flowers above ground. Food stored in the bulb starts the new plant’s growth.

Onions and garlic are perhaps the most familiar food bulbs Tulips, daffodils and narcissuses are garden flower bulbs.

Root Study

Plant root systems are essential to plants. The functions of roots are to anchor plants and absorb water and nutrients from the surrounding soil.

Plant root systems may vary in several ways. Taproots are large central roots that grow deep in the soil and it has small fibrous roots growing from it. They store food for plants to use in the winter. An example of a taproot is a carrot or a Dandelion.

Fibrous roots obtain more surface water. They absorb the food the plant requires in the form of moisture. Tip: If you look at a root closely, you will see tiny hairs on fibres through which the plant is fed. Fibrous roots are shallow roots that spread over a wide area and they branch considerably with a thread like appearance. For example, grass roots are fibrous roots.

When a seed begins to grow, the roots always grow first. Gravity causes the roots to grow down towards the earth and the stem up towards the sun.

Stem Study

Stems of plants serve many important functions. One function of a stem is to support the other plant parts that are above the ground. The stem holds up the plant’s parts towards the sun allowing the plant to receive the light energy it needs to grow. Some plants have stems that are soft and green, while others have stems that are thick and hard, like trees.

The most important function of a stem is to serve as a transport system in plants. Small tubes from the roots go up through the stems. Water and minerals are carried from the roots to the leaves of a plant. Food made in the leaves move through the tubes in the stem to other parts of the plant. For example, a potato is a portion of a plant that remains underground and swells to contain food for the plant. This specific stem is called a tuber. A corm is another kind of stem that thickens where it joins the root. This is also a food-store for the plant.

Some stems are specialized organs used to store food. Stem vegetables include celery, asparagus, sugar cane, broccoli and potatoes.

Leaf Facts

The leaf is the main food-making part of almost all plants. Leaves work like tiny food factories in a process called photosynthesis, which occurs in chloroplasts with chlorophyll. Leaves take energy from sunlight, water from soil, and carbon dioxide from the air. They change them into the food substance called glucose (a sugar), then store the glucose in plant organs as starch. Plants store the food made by leaves in their fruit, roots, seeds, stems, and even in the leaves themselves. Oxygen, as a by-product, is released into the air. All living organisms depend on oxygen for survival.

Leaves vary greatly in shape and appearance. A blade of grass, a pine needle, a fern frond, a cactus thorn, and an oak leaf, are all leaves. Leaves come in many sizes and shapes. In the pines, they are needle-like. In flowering plants, they are usually flat or thin. Leaves may be large or small, narrow or wide, long or short. They may have smooth, saw-tooth, or wavy edges. Some are thickened for water storage. Some leaves are divided into several leaflets, looking like many separate leaves. We use leaves to identify the plants because of their distinctive nature.

Most leaves have two parts, the blade and the petiole. The broad, flat part of a leaf is called the blade. The flattened shape of the typical leaf is very functional, for it provides a broad, exposed surface to collect solar energy. The petiole is the stem-like part of the leaf that joins the blade to the stem. The petiole supports the blade and turns it towards the sun. The midrib is the central vein of the leaf. The typical dicot leaf has a broad blade, a leaf petiole, and a netted venation. An axillary bud is usually present on the stem in the leaf axil. The monocot leaf, such as a blade of grass, is sheathlike at its base, attached all around the leaf node, and has parallel venation.

Leaves may be simple or compound. A simple leaf consists of one petiole and one blade. It is a single, intact structure, even though lobes or teeth may indent the margin. Trees (oak, maple, and elm) and grasses are among the many plants that have simple leaves. In a compound leaf, there is one petiole with many leaflets.