Plant Parts and Their Jobs
FoundationRoots hold the plant and take in water and nutrients, stems support and transport, leaves make food by photosynthesis, and flowers, fruits and seeds handle reproduction; a red-water experiment shows how stems carry water.
- A flowering plant has six parts: roots, stem, leaves, flowers, fruits and seeds.
- Roots hold the plant and take in water and nutrients; stems support and transport.
- Leaves use sunlight, water and carbon dioxide to make food and give off oxygen.
文體小知識：實驗觀察說明文帶我們動手做小實驗驗證知識，植物的構造和功能便看得一清二楚。
§Text Passage
1A complete flowering plant has six parts — roots, stem, leaves, flowers, fruits and seeds — and each part does a different job. Roots usually grow in the soil, holding the plant firmly and taking in water and nutrients. Some plants have one thick taproot, such as the carrot; others have masses of fibrous roots, such as lawn grass.
2The stem supports the whole plant, holding leaves and flowers up to the sunlight. Inside it are many tiny tubes, like drinking straws, that carry the water and nutrients taken in by the roots upward to every part. Leaves are the plant's food factory: green leaves use sunlight, water and carbon dioxide to make food and give off oxygen. This process is called photosynthesis.
3Flowers handle reproduction: petals attract insects that carry pollen, and the flower parts make the pollen. After pollination the ovary grows into a fruit, and the fruit holds the seeds. Seeds travel far on the wind, by water, by animals or by shooting out themselves, then sprout in a suitable place and grow into new plants.
4We can test the stem's transport job ourselves: stand a white flower or a leafy pak choi in water dyed red and leave it for a few hours. The veins and petals slowly turn red, showing that the red water travelled up through the tubes of the stem. Grow a mung bean in a pot and record it every day, and you can watch a plant's whole life story.
1Summary 重點摘要
Roots hold the plant and take in water and nutrients, stems support and transport, leaves make food by photosynthesis, and flowers, fruits and seeds handle reproduction; a red-water experiment shows how stems carry water.
2Vocabulary cards Vocabulary
Tiny water-carrying tubes in the stem that lift water upward like straws.
The process by which green leaves use sunlight, water and carbon dioxide to make food and give off oxygen.
A gas in the air, a raw material of photosynthesis, which we breathe out too.
The gas given off by photosynthesis, which we need to breathe and live.
The fine tubes on a leaf that carry water and food and hold the leaf up.
One thick root growing downward, such as the edible part of a carrot.
Many thin hair-like roots, such as those of grass.
The moving of pollen between flowers, the first step towards fruits and seeds.
The ways seeds travel away from the parent plant, such as riding the wind.
3Step by step Steps
- Step 1: Learn the six parts of a plantA complete flowering plant has six main parts: roots, stem, leaves, flowers, fruits and seeds. With a small pot plant, point out the roots, stem and leaves from the bottom up; on a flowering plant you can also find flowers, fruits and seeds. Naming these six parts first makes it easier to learn each part's job later. The flowers and trees on the school campus are ready-made teaching material; observe from the bottom up, identifying each part carefully.
- Step 2: Watch the roots at workRoots grow in the soil and do two important jobs. Gently pull up a blade of grass with its roots and you will see soil clinging tightly — proof that roots hold the plant firm in the ground so wind cannot topple it. The root tips also grow tiny root hairs, which act like drinking straws to soak up water and nutrients from the soil and send them up the stem. A plant in a flower pot sends roots out through the hole in the bottom, showing that roots keep growing towards water and nutrients.
- Step 3: The red-water experimentThe stem is the transport team, carrying water from the roots to every part. Try a small experiment: stand a pak choi in water with red colouring. After three hours the leaf veins turn red, and a cross-section of the stem shows red dots — those are the tubes that carry water. The experiment proves the tubes lift water from bottom to top for the whole plant. Cut the stem at a slant during the experiment and the red traces show up even more clearly, making the observation easier.
- Step 4: Understand photosynthesisA green leaf is like a little factory doing photosynthesis in the sunlight. Using the energy of light, it turns the water sent up by the roots and carbon dioxide from the air into food for growth, and gives out the oxygen we breathe as well. Without leaves to make food the plant would wither, and animals would lose their food too — so the leaf's job is vital. Photosynthesis also needs chlorophyll, which is why leaves are green; short of sunlight, plants grow thin and yellow.
- Step 5: Look at flowers, fruits and seedsFlowers handle reproduction, while fruits and seeds carry life onward. Cut open a ripe papaya and you will see flesh holding many black seeds: the fruit protects the seeds and helps animals carry them far away; a seed that lands in suitable soil sprouts into a new plant. Watching flowers, fruits and seeds shows how plants continue generation after generation. Fruits differ in shape — bean pods, apples and papayas — yet all do the same work of protecting and spreading the seeds.
- Step 6: Grow and recordThe best way to turn knowledge into experience is to grow a plant yourself. Plant a mung bean on wet cotton, keep it by the window for sunlight, water it daily, and measure and record the height of the stem and the number of leaves, then draw a simple growth chart. A few days later, seeing the bean sprout lets you check the textbook knowledge with your own eyes. Comparing two bean pots, one in the dark and one by the window, also shows the effect of sunlight on plant growth at the same time.
4Diagrams Diagrams
5Worked example Example
Example: Ming stood a white flower in water dyed red. Six hours later the petals had turned pink. Explain what happened.
- The stem contains many tiny tubes that carry water upward to every part of the plant.
- Once the flower stood in the red water, the water and the red colouring were drawn into the tubes of the stem.
- The tubes carried the red water all the way up through the stem to the leaves and the petals.
- The fine channels in the petals showed the red colour, so the white petals turned pink.
- Answer: The observation shows that the stem carries water upward to the leaves and flowers. The red colouring rose with the water through the tubes, reached the petals and gathered in their fine channels, so the white petals slowly turned pink.
6Common mistakes Mistakes
7Quick check Quick check
Q1What do roots do?
Q2How does the stem lift water to the leaves and flowers?
Q3What raw materials does photosynthesis need?
Q4What does the fruit do for the seeds?
Q5What does the red-water experiment prove?
8Recap Recap
- A flowering plant has six parts: roots, stem, leaves, flowers, fruits and seeds.
- Roots hold the plant and take in water and nutrients; stems support and transport.
- Leaves use sunlight, water and carbon dioxide to make food and give off oxygen.
- Flowers handle reproduction; fruits protect seeds and help them spread.
- The red-water experiment lets you see the stem's transport work with your own eyes.