Lesson 2 - Roots, Stems, and Leaves

Roots, Stems, and Leaves
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Root structure and growth

•The tip of a root is covered by the root cap.

• The root cap consists of parenchyma cells to help protect root tissues as the root grows

• Root caps are coated in a slimy
substance that reduce friction as the root grows through the soil.

Roots, Stems, and Leaves
Copyright © McGraw-Hill Education

•The layer between the epidermis and
vascular tissue is the cortex.

•Composed of ground tissue
parenchyma cells that transport or store
substances.

Roots, Stems, and Leaves
Copyright © McGraw-Hill Education

•The inner boundary of the cortex is a
layer called the endodermis.

•Each cell of the endodermis is
encircled by a waterproof strip called
the Casparian strip.

•The Casparian strip forces water
and substances to pass through the
endodermal cells instead of around
them.

Roots, Stems, and Leaves
Copyright © McGraw-Hill Education

•Directly next to the endodermis
toward the center of the root is called
the pericycle, which produces lateral
roots.

Roots, Stems, and Leaves
Copyright © McGraw-Hill Education

Types of roots

•Two major types: taproots and fibrous roots

•A taproot system consists of a thick root with few smaller, lateral-branching
roots.

•Used for food storage (beets, carrots)

•Used for deep growth to reach water

Roots, Stems, and Leaves
Copyright © McGraw-Hill Education

•Fibrous root systems have numerous branching roots that are about the same
size and grow from a central point.

•Other root types are adapted to diverse environments

•Pneumatophores are adapted to supply oxygen to roots submerged in
water.

•Adventitious roots form unusual support structures.

Roots, Stems, and Leaves
Copyright © McGraw-Hill Education

Stems

Stem structure and function

•Some stems are soft, flexible, and capable of photosynthesis – herbaceous
stems

•Other stems are rigid and fibrous – woody stems

•Main function is support of leaves and reproductive costumes

Roots, Stems, and Leaves
Copyright © McGraw-Hill Education

Stems

Growth of a stem

•The apical meristem produces cells that increase the length of a stem.

•As plants grow taller, an increase in stem diameter provide additional support.

•The vascular cambium produces additional cells to increase stem diameter

•These cells form annual grown rings in some plants, particularly trees,
which can be used to age the organism.

Roots, Stems, and Leaves
Copyright © McGraw-Hill Education

Stems

Types of stems

•Stems have adaptations that help plants survive

•Store excess food

•Withstand drought, cold, or heat

•Some plants have underground stems (tubers, bulbs, rhizomes)

Roots, Stems, and Leaves
Copyright © McGraw-Hill Education

Leaves

Leaf Structure

•The main function of leaves is
photosynthesis, and they have many
adaptations to optimize this purpose.

•Most leaves have a flattened portion
called the blade with a large surface
area.

•The blade is attached to the stem by
a stalk called a petiole.

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Leaves

Leaf structure

•The internal structure of most leaves
is well-adapted for photosynthesis.

•The palisade mesophyll is composed
of tightly packed cells with many
chloroplasts.

•The spongy mesophyll consists of
irregularly shaped cells with spaces
in between, allowing gases move
between the spaces

Roots, Stems, and Leaves

Roots, Stems, and Leaves
Copyright © McGraw-Hill Education

Leaves

Gas exchange and transpiration

•The epidermis contains stomata, pores that allow for gas exchange.

•Stomata are important in the transportation of water from the roots through the
vascular tissue.

•Water evaporates through the stomata in a process called transpiration that
helps pull the water column upward.

Roots, Stems, and Leaves
Copyright © McGraw-Hill Education

Leaves

Characteristics of
leaves

•Leaves differ in size,
shape, arrangement
on the stem, and
venation

Roots, Stems, and Leaves
Copyright © McGraw-Hill Education

Leaves

Leaf modifications

•Leaves have functions beyond photosynthesis.

•In cacti, leaves have been modified into spines to prevent predation by animals.

•Pitcher plants modify leaves into cylinders that fill with water and trap insects.

•Some leaves produce toxic chemicals to deter predation.