【Science】1st Year Junior High: The Structure and Function of Plant Bodies

Hello everyone! Today, we are going to explore "the structure and function of plant bodies" together.
Do you ever think, "Plants don't move and seem a bit boring"? Actually, there are some incredible mechanisms constantly at work inside a plant to keep it alive. Once you master this chapter, you’ll definitely look at the flowers on the side of the road and the vegetables on your dinner plate in a whole new way!
It might feel a bit tricky at first, but don't worry—we’ll take it one step at a time using relatable examples.

1. Flower Structure and Pollination

For plants, the flower is a very important place for "passing on the next generation (seeds)."

Basic Parts of a Flower

Most flowers consist of the following parts, starting from the outside:

  • Sepals: Protect the inside of the flower while it is still a bud.
  • Petals: The colorful parts that attract insects.
  • Stamens: The male part. The tip is called the anther, which contains pollen.
  • Pistil: The central part, consisting of the stigma, style, and ovary.

How Seeds are Formed

When pollen from the stamen lands on the stigma of the pistil, it is called pollination.
After pollination, the ovary (the swollen part at the base of the pistil) develops into a fruit, and the ovule inside the ovary develops into a seed.

【Pro-Tip: This will be on the test!】
Remember what each part turns into as a pair!
・Ovary → Fruit
・Ovule → Seed

【Fun Fact】
Flowers are brightly colored and have nice scents to tell insects, "There’s nectar here!" and to get them to carry pollen (to help with pollination). It’s a clever plant strategy!

2. Classification of Plants (Seed Plants)

Plants are divided into seed plants (which reproduce by seeds) and those that do not. Seed plants are further divided into two groups.

① Angiosperms

Plants in which the ovules are enclosed within an ovary. Most flowers you see every day, such as rapeseed, cherry blossoms, and azaleas, fall into this category.

② Gymnosperms

Plants that do not have an ovary, meaning the ovules are exposed. Representative examples include pine, cedar, ginkgo, and cycad trees.
*The term "gymno-" means "naked," which is why they are called this—their ovules are "naked" or exposed.

【Common Mistake】
People often think pine trees don't have "flowers," but they do! They have "female flowers" and "male flowers." However, they lack petals and sepals.

3. Leaf Structure and Function (Photosynthesis and Respiration)

For a plant, the leaf serves as both a "cafeteria" and a "lung."

① Photosynthesis

The process by which plants use light energy to create their own nutrients (such as starch).
Location: Takes place in green particles inside the cell called chloroplasts.
Ingredients: Water + Carbon dioxide
Result: Nutrients (Starch) + Oxygen

You can think of it like this equation:
\( Water + Carbon\ dioxide + Light\ energy \rightarrow Nutrients + Oxygen \)

② Transpiration

The phenomenon where water absorbed by the roots evaporates as water vapor from small pores on the underside of leaves, called stomata.
This helps the plant regulate its temperature and creates the force needed to pull water up from the roots.

③ Respiration

Just like humans, plants breathe 24 hours a day: they take in oxygen and release carbon dioxide.
We often think of plants as "giving off oxygen," but that’s only because during the day, they perform photosynthesis so actively that the amount of oxygen released through photosynthesis is greater than the carbon dioxide released through respiration.

【Point: Difference between Day and Night】
・Day: Photosynthesis > Respiration (overall oxygen is released)
・Night: Respiration only (carbon dioxide is released)

4. Structure of Stems and Roots (The Water Pathways)

Inside a plant, there are tube-like structures similar to our "blood vessels." These are called vascular bundles.

Xylem and Phloem

  • Xylem: Tubes that transport water and minerals absorbed by the roots.
  • Phloem: Tubes that transport nutrients made in the leaves.

Root Structure

At the tips of roots, there are many hair-like structures called root hairs.
These increase the surface area of the roots, allowing the plant to absorb water and nutrients efficiently.

5. Monocots and Dicots (Summary of Classification)

Angiosperms are divided into two types based on the number of leaves that appear when the seed germinates (cotyledons). This is a crucial point that often appears on tests!

● Dicots (Dicotyledons)
  • Cotyledons: 2
  • Leaf veins: Net-like (reticulate)
  • Roots: Taproot and lateral roots (a thick main root)
  • Vascular bundles: Arranged in a ring
  • Examples: Rapeseed, Sunflower, Balsam
● Monocots (Monocotyledons)
  • Cotyledon: 1
  • Leaf veins: Parallel
  • Roots: Fibrous roots (tangled and bushy)
  • Vascular bundles: Scattered randomly
  • Examples: Corn, Rice, Lily

【Memorization Tip】
Remember that everything about a "Monocot" is simple! The veins are straight (parallel), the roots are bushy (fibrous), and there is only one cotyledon. It’s easier to remember them as a set.

Finally: Quick Check!

1. After pollination, the ovary becomes (　　), and the ovule becomes (　　).
2. The process where plants use light to create nutrients is called (　　).
3. The tubes that transport water are (　　), and the tubes that transport nutrients are (　　).
(Answers: 1. Fruit, Seed / 2. Photosynthesis / 3. Xylem, Phloem)

Great work! Plant structures might look complicated at first glance, but it becomes much easier to understand once you ask yourself, "Why does it have this shape?" (e.g., "Root hairs are for absorbing lots of water"). Try reading this through a few times to build up a clear mental image. I’m cheering for you!