Reproduction and Growth of Plants Chapter Notes | Science for Grade 6 PDF Download

Introduction

Plants are amazing living things that grow and make new plants in different ways. This chapter explores how plants, like the purple tansy, reproduce to create new plants and what helps or affects their growth. You will learn about the structures plants use to reproduce, how they spread their seeds, and the factors that help them grow strong and healthy. From seeds to spores, and from sunlight to water, this chapter explains the exciting ways plants live and thrive in nature.

How do different types of plants reproduce?

Plants can make new plants in two main ways: asexually, sexually, or sometimes both.

• Asexual reproduction happens when a part of a plant grows into a new plant without seeds.
• Sexual reproduction happens when a plant's male cell (sperm) joins with a female cell (egg).
• The way a plant reproduces depends on the structures it has, like flowers or cones.

Seedless Plants

• Not all plants grow from seeds; some use spores instead.
• Seedless plants, like mosses and ferns, were some of the first plants on Earth.
• These plants grow from tiny spores, not seeds, to make new plants.

Seed Plants

• Seed plants are divided into two groups: flowering plants and flowerless seed plants.
• Both types use sexual reproduction to make seeds.
• Plants produce pollen grains, which contain sperm, and female structures with eggs.
• Pollination happens when pollen lands on a female plant part of the same species.
• If pollen joins with an egg, a seed forms after fertilization.
• In flowerless plants, male cones make pollen, and female cones hold eggs.
• In flowering plants, the pistil is the female part, and the stamen is the male part.

How can plants find mates and spread seeds if they cannot move?

• Plants cannot move, but they have ways to reproduce and spread seeds.
• Pollination can happen in different ways, like through wind, animals, or insects.
• Seeds need to spread to places with light, water, food, and space to grow.

Seeds on the Move

• Seeds travel in different ways to reach new places for growth.
• Some seeds are light or have structures like parachutes or propellers to fly in the wind (e.g., milkweed, maple).
• Some seeds have waterproof layers to float on water (e.g., water lily, mangrove).
• Some seeds are eaten by animals or have hooks to stick to fur or feathers (e.g., burdock).

Buzzing About Climate Change

• Bees help plants reproduce by carrying pollen from flower to flower while collecting nectar.
• Climate change affects when plants flower and when bees are active.
• Flowering plants and pollinators, like bees, evolved together to time their cycles.
• Some plants and pollinators use the same environmental cues, like temperature, to stay in sync.
• Other plants and pollinators use different cues, like snow melt or air temperature, which can cause mismatches.
• Climate change, like rising temperatures from urbanization and greenhouse gases, can change flowering times.
• These changes may disrupt plant-pollinator relationships, affecting crops and ecosystems.

What factors affect how plants can grow?

• Plants need certain conditions to grow, like light, water, and the right temperature.
• Environmental factors, like high salinity, cold, heat, or drought, can affect plant growth.
• Tropisms are ways plants grow toward or away from something.
• Phototropism is when plants grow toward or away from light, using a light-sensing chemical.
• Thigmotropism is when plants grow in response to touch, like vines climbing a fence.
• Gravitropism is when stems grow upward against gravity, and roots grow downward toward gravity.
• Genetic factors, passed from parent plants, decide traits like flower color or where flowers bloom.

A Closer Look: Growing Plants in Space

• Greenhouses on Earth let sunlight in and keep heat inside to help plants grow in cool climates.
• In space, plants lack resources like light, water, and proper temperature.
• Scientists use plant growth chambers to create Earth-like conditions for growing plants in space.
• These chambers help grow plants for food in space environments, like on the Moon.