Plants Structure

Structure and Functions of Leaves, Stems and Roots in a Plant

Features of Plants (5 reasons)

• Unique in their morphology (appearance) unlike animals and tissues

• Has unique tissues and organs and the cells are different from animal cells

• Has rigid cells walls that has cellulose, it one of the most abundant plant-derived molecules on Earth

• Also has chloroplasts with chlorophyll and have vacuoles unseen in animals

  • Chloroplasts/chlorophyll are found in leaves and stems primarily

Plant vs Animal Cells

3 things only found in plant cells

• Chloroplasts

• Vacuole

• Cell wall

Differences in Plant Cells

• Smaller number of ribosomes

• Larger vacuole

• Less mitochondria

• Has a membrane inside a cell wall

Cell Wall/Chloroplasts/Vacuole

Lists of terms

• Cuticle

  • Outer waxy layer on leaves

  • Reduces water loss

• Cell wall

  • Multi-layered structure

  • Protects cell

• Middle lamella

  • Separates primary and secondary cell wall

• Plasmodesmata

  • Cytoplasmic connections between cells

• Cellulose

  • Glucose molecules forming a long chain

Cell Wall structure

What is cellulose made up of

• Made of glucose molecules

• Alternating Oxygen bond in between each molecule

Components of the cell wall are cross-linked

Plant Cell Wall Structure

• Primary cell wall contains cellulose

  • Long chain of glucose molecules

• Secondary cell wall has

  • Hemi cellulose and lignin

    • Provides cell wall strength and thickening

• Secondary growth

  • Seen in trees due to the thickening of the secondary cell walls

  • It is the thickening of the secondary cell wall

• Between individual cells

  • Middle lamella holds cells together

  • Contains pectin and calcium

Cell to Cell communication

• Has a connection called plasmodesmata

  • Allows for communication and signals to occur between cells and transport of materials

  • Intercellular pores connecting each other

Whole Plant Structure

• All plants have shoots that grow above the ground and roots that grow below ground

• Shoots

  • consist of a stem and leaves and bear flowers and seeds

• Roots

  • Function as storage organs and are most important for absorption of water and nutrients

  • Create a large surface area

Functions of Leaves

• Primary site for photosynthesis

  • Sugar is formed from carbon dioxide and water and oxygen is produced

• Leaves may be simple or compound in structure

• Has an upper epidermis and a lower epidermis. In between are mesophyll cells

  • Palisade mesophyll and spongy mesophyll

    • Palisade mesophyll has many chloroplasts for photosynthesis

    • Spongy mesophyll has many air cavities for gas exchange

• Leaves has cuticle on the surface that contain waxes (hydrophobic) that reduces water loos (transpiration)

Organization of leaf tissues

Outer layer

• Cuticle

Underneath cuticle

• Epidermis, Upper or lower

In-between Upper and Lower epidermis

• Palisade mesophyll

• Spongy mesophyll

Adaptions of Leaves to Changing Environments

• Spines

  • To reduce water loss from transpiration

• Tendrils

• Reproductive leaves

• Storage leaves

• Bracts

Function of Stems

• Provide Physical support to the plant and are also involved in movement of water and nutrients up the plant through the vascular system (xylem and phloem)

• Allows for continued growth through the apical meristem

• Contain axillary buds that give rise to side shoots

• Can be used for storage of food and water

• Allow for lateral growth to increase width of the stem

• Has roots coming out

Shoots grow through Apical Buds and Axillary Buds

In the Shoot Tips is the Apical meristem, a region of actively dividing cells

Modifications of Stems for Different purposes

• Rhizomes can be found in ginger, turmeric and ginseng plants

  • A horizontal underground plant stem capable of producing the shoot and root systems of a new plant

  • Used for storage of nutrients

• Stolon (strawberry plant)

• Tubers

  • Starch

  • The eye of a potato is the axillary bud

  • A potato is a tuber

Continued plant growth occurs through meristems

4 types of meristematic tissues

• Apical (shoot and root)

• Axillary and lateral meristem (vascular)

Meristem

• Actively growing regions found at the tips of shoots and roots of plants that allow for continued growth

• Growth of side shoots from stems is also due to axillary bud meristems

• Expansion of width of stems (lateral growth) is due to the activity of lateral meristems, especially cambium

Functions of Roots

• Anchor the plant/tree in the soil

• Absorb water and nutrients from the soil

• Roots have a large surface area due to root hairs

• Continued growth occurs through the root meristems

• Can be used for storage of nutrients

Types of Roots

• Prop roots

• Buttress roots

• "strangling" aerial roots

• Pneumatophores

Structure of a Carrot Root

• The entire carrot is a root

Things in Roots

• Vascular cylinder

• Cortex

• Epidermis

• Root hair

• The activity in the root apical meristem causes roots to grow

Know the tissues and what they do

Tissue Types in Plants

Dermal

• Found on the outside layer of plant tissues, provides protection to the plant

  • E.x Epidermis

Meristematic

• Found at the growing tips

• E.x shoots

Ground

• Forms the Bulk of the plant

• Underneath the dermal

• There are 3 types

  • Parenchyma

  • Collenchyma

  • Sclerenchyma

Vascular

• In the middle of the plant

• There are 2 types

  • Xylem

  • Phloem

Ground Tissues

• Parenchyma

  • The most common

  • There are cells in leaves and tubers. Constitute living cells

  • Involved in producing sugar during photosynthesis

    • Contain chloroplasts

  • Can store food (starch) in roots tubers and fruit

  • Have thin walls and large vacuoles

• Collenchyma

  • Do not store food

  • Constitute living cells

  • Function is to provide structural support to plants

  • They have thick walls

• Sclerenchyma

  • Non-living cells

  • Are thick-walled

  • Function in providing support and rigidity to plants

Vascular Tissue

• Function for transport

  • Xylem

    • Moves water and nutrients up the plant from roots through stems to leaves

    • Consists of cells called tracheid and vessel elements

    • Non-living cells

  • Phloem

    • Moves sugar and water solution from leaves to down the plant

    • Usually moves down the plant

    • Consists of sieve tube elements and companion cells

    • Are living cells

Vascular Cambium

• Ring of actively dividing cells found separating the xylem and phloem

• Cell divisions result in the formation of a secondary xylem and secondary phloem

• It permits secondary (lateral growth)

• Ring of cambium can turn into xylem or phloem cells

• The activity of vascular cambium causes the growth rings in trees

Dendrochronology

• Study of tree rings

• Each ring is 1 year of growth

• Wider the ring, more nutrient the tree had that year

Parts of a plant

Root system

• Taproot

  • Large, central and dominant root where other root sprout laterally

• Lateral (branch) roots

  • Sprout laterally from the taproot

Stem System

• Stem

  • Plant axis that bears buds and shoots with leaves. It is above ground that provides support for leaves and buds

• Leaf

  • Usually flattened green outgrowth from the stem

    • Blade

      • Thin flat part of a leaf

    • Petiole

      • Stalk that attaches a leaf to the plant stem

• Axillary bud

  • Precursor of a branch or lateral shoot, formed at the junction between a leaf and stem

• Vegetative shoot

  • Parth that comes up out of the ground consisting of the stem and leaves of the plant

• Apical bud

  • Located at the tip of the stem, responsible for the elongation and primary growth of the stem

• Internode

  • Section of stem between nodes

• Node

  • Area where leaves begin to grow. Where the points on a stem where the buds, leaves, and branching twigs originate. Where the petiole and leaf grow from

• Reproductive shoot (flower)

  • Contains reproductive parts of the plant