The glucose produced provides energy for growth, reproduction, and all other life processes. Animals and other consumers depend on plants because they cannot produce their own food.

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Figure 2. Through photosynthesis, plants convert sunlight into chemical energy while releasing oxygen into the atmosphere.

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The Role of Chlorophyll

Plants appear green because they contain chlorophyll.

Chlorophyll is the green pigment found inside chloroplasts.

Its job is to absorb light energy from the Sun.

This energy powers photosynthesis.

Chlorophyll absorbs:

• Red light
• Blue light

It reflects:

• Green light

This reflected green light is why most plants appear green to our eyes.

Without chlorophyll, photosynthesis could not occur.

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Figure 3. Chlorophyll inside chloroplasts captures light energy needed for photosynthesis.

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Cell Walls and Vacuoles

Plant cells have two important structures that animal cells do not.

Cell Wall

The cell wall surrounds the cell membrane.

It is made mainly of cellulose.

Functions:

• Provides support.
• Maintains cell shape.
• Protects the cell.
• Helps plants remain upright.

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Large Central Vacuole

Most plant cells contain a large central vacuole filled with water.

Functions:

• Stores water.
• Stores nutrients.
• Maintains internal pressure.
• Helps support leaves and stems.

When plants lose water, vacuoles shrink and plants begin to wilt.

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Major Groups of Plants

Scientists classify plants into several major groups.

Mosses (Bryophytes)

Characteristics:

• Small
• No true roots
• No flowers
• Reproduce using spores
• Live in moist environments

Examples:

• Moss
• Liverwort

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Ferns (Pteridophytes)

Characteristics:

• Have roots, stems, and leaves
• Reproduce using spores
• Do not produce flowers or seeds

Examples:

• Bracken fern
• Maidenhair fern

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Gymnosperms

Characteristics:

• Produce seeds
• Seeds are not enclosed within fruits
• Usually bear cones

Examples:

• Pine trees
• Spruce trees
• Fir trees

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Angiosperms (Flowering Plants)

Characteristics:

• Produce flowers
• Produce fruits
• Seeds are enclosed inside fruits

Examples:

• Roses
• Oak trees
• Sunflowers
• Apple trees
• Grasses

Angiosperms are the largest and most diverse group of plants on Earth.

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Figure 4. Plants are divided into major groups based on their reproductive structures and evolutionary history.

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Why Plants Are Important

Plants play essential roles in ecosystems.

They:

• Produce oxygen.
• Remove carbon dioxide from the atmosphere.
• Form the base of most food chains.
• Provide habitats for wildlife.
• Prevent soil erosion.
• Help regulate Earth's climate.
• Supply food, medicines, fibres, and building materials.

Without plants, nearly all ecosystems would collapse.

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Comparing Plants with Animals

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Worked Example

Question

Classify each statement as True or False.

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Real-World Connection

Much of the world's food comes directly or indirectly from flowering plants. Crops such as rice, wheat, maize, potatoes, fruits, and vegetables all belong to the angiosperms. Even meat, milk, and eggs depend on plants because farm animals obtain their energy by eating grasses and other plant materials.

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Did You Know?

The giant sequoia (Sequoiadendron giganteum) is one of the largest living organisms on Earth, growing to heights of over 90 metres and living for more than 3,000 years. At the other extreme, some flowering plants, such as duckweed, are only a few millimetres across, making plants one of the most diverse groups of organisms on the planet.

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Key Terms

Autotroph – An organism that makes its own food using sunlight or chemical energy.

Cell wall – A rigid outer layer surrounding plant cells, made mainly of cellulose.

Cellulose – A strong carbohydrate that forms plant cell walls.

Chlorophyll – The green pigment that absorbs light energy for photosynthesis.

Chloroplast – The organelle where photosynthesis takes place.

Eukaryote – An organism whose cells contain a nucleus and membrane-bound organelles.

Multicellular – Made of many cells.

Photosynthesis – The process by which plants use sunlight to produce glucose from carbon dioxide and water.

Producer – An organism that makes its own food and forms the base of most food chains.

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Key Takeaways

• Plants are multicellular, eukaryotic organisms that produce their own food through photosynthesis.
• Chlorophyll inside chloroplasts captures light energy needed for photosynthesis.
• Plant cells have cellulose cell walls and large central vacuoles that provide support and structure.
• The four major groups of plants are mosses, ferns, gymnosperms, and angiosperms.
• Plants are essential because they produce oxygen, remove carbon dioxide, provide food, and support nearly every ecosystem on Earth.