Plants

What is a Plant?

• Plants are– Autotrophs– Eukaryotes– Multi-cellular

What is a Plant?

• Most plants are autotrophs, which means that they make their own food.

• Sunlight provides the energy for the plant food-making process, which is known as photosynthesis.– During photosynthesis, plants use carbon dioxide

and sunlight to produce food and oxygen.

What is a Plant?

• Plants are eukaryotes, which means that they have a nucleus.

• Although plants vary greatly in size, they all contain multiple cells, which are organized into tissues.

What is a Plant?

• Unlike animal cells, plant cells contain a cell wall which protects the cell.

• Plant cells also contain chloroplasts which capture sunlight and undergo photosynthesis. This is what gives plants their green color.

Living on Land

• Most plants live on land.• In order to be able to live on land, plants must

be able to – Obtain water and nutrients– Retain water– Transport materials– Support their bodies– Reproduce

Living on Land

• Most plants use their roots to suck water and nutrients up from the ground.

Living on Land

• Most plants retain water by having a waxy, waterproof layer that covers their leaves called a cuticle.

Living on Land

• Like all organisms, plants must be able to transport materials to different parts of its body.

• Larger plants have transporting tissue called vascular tissue. Vascular tissue is a system of tubelike structures where water and other substances are transported through the plant.

Living on Land

• For small plants, support is not an issue, but for larger plants, rigid cells walls and vascular tissue strengthen and support the plant’s bodies.

Living on Land

• All plants undergo sexual reproduction.• Fertilization occurs when the sperm cell unites

with an egg cell creating a fertilized egg, or zygote.

The Origin of Plants

• The oldest plant fossils are about 400 million years old.

• These fossils already had many adaptations for land life, including vascular tissue.

The Origin of Plants

• Land plants and green algae have very similar forms of chlorophyll, and their genetic material is similar.

• Because of this, many biologists believe plants evolved from ancient green algae.

Plant Life Cycles

• Plants have complex life cycles that include two different stages:– The sporophyte stage– The gametophyte stage

Plant Life Cycles

• The sporophyte stage– The plant produces spores, which are tiny cells

that can grow into new organisms.– The spore then develops and enters the

gametophyte stage.

Plant Life Cycles

• The gametophyte stage– The plant produces two kinds of sex cells: sperm

cells and egg cells.– These cells then join and create a zygote.– The zygote grows and develops into a sporophyte,

which creates more spores, starting the cycle over again.

Classification of Plants

• Scientists classify plants into two major groups:– Nonvascular plants– Vascular plants

Nonvascular Plants

• Nonvascular plants do not have a well-developed system of tubes for transporting water and other materials.

• They are low-growing and do not have roots for absorbing water from the ground.

Nonvascular Plants

• Nonvascular plants obtain water and materials directly from their surroundings.

• The materials then pass from one cell directly to another.

• This type of transport is slow and does not go very far.

Nonvascular Plants

• Nonvascular plants normally live in damp, shady places so that they can easily access water.

• Nonvascular plants have very thin cell walls and cannot grow more than a few centimeters tall.

Nonvascular Plants

• There are three major groups of nonvascular plants:– Mosses– Liverworts– Hornworts

Mosses

• Mosses are the most diverse group of nonvascular plants, with more than 10,000 species.

Mosses

• The familiar green, fuzzy moss is the gametophyte generation of the plant.

• Thin, rootlike structures called rhizoids hold the moss and absorb water and nutrients.

• The sporophyte generation then grows up out of this in long, slender stalks, with a capsule at the end that contains spores.

Liverworts

• There are more than 8,000 species of liverworts.

• Liverworts are named because they grow in the shape of a human liver.–Wort means “plant”.

• Liverworts grow as a thick crust on moist rocks or soil along the sides of streams.

Hornworts

• There are less than 100 species of hornworts.• Hornworts are named after the sporophyte

generation that appear as slender, curved structures that look like horns.

• Hornworts are found in moist soil, normally mixed with grass plants.

Vascular Plants

• Vascular plants have true vascular tissue, which allows transport of materials quickly and efficiently through the plant’s body.

• Vascular tissue also provides strength, stability, and support allowing vascular plants to grow tall.

Vascular Plants

• Vascular plants can be broken down into two groups:– Seedless plants– Seed Plants

Seedless Plants

• Seedless vascular plants do not produce seeds. Instead they produce spores.

• Because they produce spores instead of seeds, these plants must live in moist surroundings, so that the sperm can swim toward the egg during the gametophyte stage.

Seedless Plants

• Seedless vascular plants have very strong cell walls, which gives them strength and stability.

• This allows them to grow much taller than nonvascular plants.

Seedless Plants

• Seedless plants are broken down into three groups:– Ferns– Club Mosses– Horsetails

Ferns

• There are more than 12,000 species of ferns, making them the most diverse seedless vascular plant.

• Ferns range in size from a few millimeters to 5 meters tall.

Ferns

• Like all vascular plants, ferns have stems, roots, and leaves.

• The stems of most ferns are underground, while the leaves grow upward from the top of the stems and the roots grow downward from the bottom of the stems.

Ferns

• The fern’s leaves, or fronds, are divided into many smaller parts, that look like small leaves.

Ferns

• The regular fern is the sporophyte generation of ferns and develops spores on the underside of its fronds.

• The gametophyte generation appears as tiny plants low to the ground.

Club Mosses

• There are very few species of club mosses.• Club mosses are not the same as regular moss

because it has vascular tissue.• Club mosses grow in moist woodlands and

near streams.

Horsetails

• There are only about 20 species of horsetails on Earth today.

• The stems of horsetails are jointed and have needlelike branches coming out of the joints.

• Horsetails get their name because they resemble a horse’s tail.