【Shanghai Textbook Edition】Junior High School Science, Grade 8, Semester 2: The Prelude from Flower to Fruit – Floral Structure, Pollination, and Double Fertilization

From Blossoms to Fruits: A Precise Symphony of Life

Sexual reproduction is the core of higher plant propagation. This process is not only the most intricate morphological transformation in a plant's life cycle but also a prerequisite for subsequent fruit development and seed formation. Acomplete flowertypically includes structures such as the pedicel, receptacle, sepals, petals, stamens, and pistils.

Core Physiological Mechanisms

Pollination: The process after flowering where pollen is released from the anthers of the stamens and lands on the stigma of the pistil. It is divided into self-pollination (e.g., peas) and cross-pollination.
Double Fertilization: The hallmark of angiosperms. One sperm fuses with the egg cell to form a zygote (2N), while another sperm fuses with two polar nuclei to form a triploid primary endosperm nucleus (3N). Since two fertilization events occur simultaneously within the ovule, it is called double fertilization.

Experimental Procedure: Artificial Assisted Pollination

1. Emasculate and bag before flowering; 2. Collect target pollen; 3. Apply pollen to the stigma using a soft brush; 4. Continue bagging after pollination to observe and ensure genetic purity of the parent.

QUESTION 1

When observing floral structure, if a flower contains only stamens or only pistils, what is this type of flower called?

Complete flower

Unisexual flower

Bisexual flower

Asexual flower

QUESTION 2

Which of the following descriptions about entomophilous and anemophilous flowers is correct?

Anemophilous flowers typically have bright corollas and sweet nectar

Entomophilous flowers usually have abundant, lightweight pollen suitable for wind dispersal

Anemophilous flowers often have feathery or branched stigmas to capture pollen

Entomophilous flowers usually lack fragrance and rely on wind for pollination

QUESTION 3

In double fertilization, what structure will the fertilized polar nucleus develop into?

Embryo

Pericarp

Endosperm

Seed coat

QUESTION 4

What would be the impact on experimental results if stamens were not removed or the flowers were not bagged after artificial pollination?

The ovary development cannot be observed

Self-pollination may occur or contamination by external pollen may happen

The plant will wilt directly

QUESTION 5

Based on 'inductive reasoning,' what conclusion did we draw after observing various complete flowers such as peach and broad bean flowers?

All plants must have petals

A complete flower typically consists of a pedicel, receptacle, sepals, petals, stamens, and pistils

All plants reproduce through insect pollination

Comprehensive Analysis of Plant Reproduction and Development

From Seed Structure to Propagation Techniques

A research team is studying different plant reproductive strategies and germination conditions, including comparisons between broad beans and corn, as well as applications of techniques like cuttings in agriculture.

1. What are the main differences in morphological structure between broad bean seeds and corn seeds?

Answer:
Broad beans are dicotyledons: their seeds have two cotyledons, no endosperm, and nutrients are stored in the cotyledons. Corn is a monocotyledon: its seeds have one cotyledon, possess endosperm, and nutrients are stored in the endosperm. Moreover, what we commonly call a 'corn seed' is actually a caryopsis, where the pericarp and seed coat are fused together.

2. What changes occur sequentially during seed germination? How do germination processes differ between monocots and dicots?

Answer:
Germination sequence: water absorption → increased respiration → nutrient conversion → radicle breaks through the seed coat to form root → hypocotyl elongates → plumule develops into stem and leaves. Both require water, air, and suitable temperature. Differences lie in nutrient sources: dicots use cotyledons, monocots use endosperm; the emergence of cotyledons also varies.

3. Provide examples of fruits' roles in seed dispersal and explain why excess leaves are removed during cuttings.

Answer:
Fruits protect seeds and aid in dispersal: fleshy fruits attract animals for consumption (e.g., burrs clinging to fur, grapes eaten), while dry fruits disperse via mechanical force. Removing excess leaves during cuttings reduces transpiration, minimizes water loss, and increases survival rate before rooting.

4. What is the role of setup 5 (optimal condition group) in seed germination experiments? Which plants commonly use vegetative propagation?

Answer:
Setup 5 serves as the control group, providing a standard environment to compare variable effects. Commonly propagated vegetatively are: potatoes (tubers), strawberries (runners), sweet potatoes (roots), roses (cuttings), and apple trees (grafting).