9.1Chapter 9: Plants and Photosynthesis

What do we know about plants? — Alhussan Biology - Stage 9 Revision Notes & Topical Questions

5 min read 8 parts Lesson 1 of 9 2 quizzes

📚 Alhussan Biology - Stage 9 Hub / Topical Revision

0%read

Lesson summary

9.1 What do we know about plants?

Other uses
Plant science
Common features
Palisade cells
Root hair cells
Guard cells

Section 1 of 8Why plants matter

Food

Food plants make carbohydrates using energy from the Sun and carbon dioxide from the atmosphere.
They are the producers in food chains and webs all over the world.
Crops are the source of most human food, both directly and as animal feed.

Other uses

Other uses plants are part of the water cycle and give materials for medicines, clothing, building and biofuels.

Plant science

Plant science biologists study plant structure, breeding and genetic material, nutrients, pests and diseases to improve crops.

Section 2 of 8Organs of a flowering plant

A flowering plant has a root system and a shoot system, and each organ is made of tissues, which are groups of similar cells.

2Roots

Roots they anchor the plant and absorb water and mineral ions through root hairs, which give a large surface area.

3Stem

Stem it supports the leaves, flowers and fruit and holds them in the light.
It contains xylem and phloem that carry water and sugars.

4Leaves

Leaves they are the main organs of photosynthesis, using chlorophyll to capture energy from the Sun.
They are flat and thin with a large surface area, and stomata let gases in and out.

5Flowers

Flowers they are the organs of sexual reproduction, producing pollen and ovules and later forming fruits and seeds.
They appear only at certain times in the life cycle.

Organ	Main function
Root	Anchorage; absorption of water and minerals
Stem	Support; transport
Leaf	Photosynthesis; gas exchange
Flower	Reproduction

Section 3 of 8Plant cells and their features

Plant cells and their features

Common features

Common features plant cells have a cell wall of cellulose, a large permanent vacuole and chloroplasts in green parts.

Palisade cells

Palisade cells they have many chloroplasts and are packed at the top of the leaf to absorb light.

Root hair cells

Root hair cells they have no chloroplasts but a long extension that increases surface area for absorption.

Guard cells

Guard cells they open and close the stomata.

Section 4 of 8Biomass

Biomass

Biomass the mass of living material, such as a plant, an animal or an ecosystem.

Gaining biomass

Gaining biomass plants build carbon from the air into sugars by photosynthesis, then convert them to starch, cellulose, proteins and fats.
Most of the dry mass of a plant comes from carbon dioxide in the air, not from the soil.
Water from the soil supplies hydrogen and oxygen atoms.

Measuring biomass

Measuring biomass use dry mass, found by heating the plant gently in an oven until the mass no longer changes.
Fresh mass varies with water content, so it is not reliable.

Section 5 of 8Investigating plant growth

1Methods

Methods measure height or leaf area every few days, or dry the plants and find their mass at the end.

2Van Helmont's willow experiment (1600s)

Van Helmont's willow experiment (1600s) a 2.3 kg willow grew in 90 kg of soil for five years and reached 76 kg while the soil mass hardly changed.
He concluded that the plant came from water.
We now know the main source of the extra mass is carbon dioxide.

Section 6 of 8Crop yields

Trend

Trend each crop produces more now than in 1961, and the yield of some crops, such as maize and wheat, has more than doubled.

Causes

Causes the extra food results from scientists learning more about plants, along with the crop plant, farming methods, fertilisers and climate.

Section 7 of 8Key terms

Term	Meaning
Organ	A part of an organism made of tissues that does a specific job.
Tissue	A group of similar cells.
Biomass	The mass of living material.
Chlorophyll	The green pigment that captures light for photosynthesis.
Stoma	A pore in a leaf that allows gases in and out.
Xylem	Tissue that carries water and mineral ions in a plant.