Plant Systems Part II

Plant Tissues

• A tissue is a group of cells working together to perform a similar function.– The cells in tissues are specialized to perform specific

functions. – All these cells develop from unspecialized cells during

cellular differentiation Recall: what were unspecialized cells called in animals?Stem Cells!

• In plants, these cells are not called stem cells – they are called meristematic cells

• A region of a plant that is rich in meristematic cells is called the meristem region

(see video on plant growth and meristematic cells)

Tissue Systems

• Plants have 3 major tissue systems:

1. Dermal• Covers outer surface of plant

2. Vascular• Found in every root, shoot and

leaf• System is continuous (all plant

parts joined by vascular tissues)

3. Ground• All other tissues

Dermal Tissue System

Dermal Tissue System

Epidermal TissueThin layer of cells

covering all non-woody surfaces of a plant

Periderm Tissue

Tissues on the surface of the plant that

produce bark on stems and roots

Dermal Tissue System

Cells of the Dermal tissue system:– Epidermal root cells have extensions (root hairs) to absorb

water and minerals– Epidermal leaf cells produce a layer of wax to waterproof

surface– Some have developed for defense purposes

Vascular Tissue System

• This is the transportation system that moves water, minerals and other chemicals around the plant

• All vascular tissues are connected

Vascular Tissue System

Vascular Tissue System

Xylem

Transports water and dissolved minerals from the roots to the leaves

and stems

Phloem

Transports dissolved food materials and

hormones throughout the plant

Vascular Tissue System

Xylem– Transports water and dissolved

minerals upwards from the roots– Cells are hollow tubes with rigid walls• No cytoplasm, nucleus or organelles

(allows for easier transportation of water)

– MATURE xylem cells are not considered living tissue

Vascular Tissue System

Phloem– Transports sugars produced by

photosynthesis (and hormones)– Phloem can move sugars downwards

from the leaves and stems or upwards from the roots

– Phloem cells are alive when functioning

Ground Tissue System

• The ‘filler’ between dermal and vascular tissues• Functions:– In green parts of plant, they manufacture nutrients

via photosynthesis– In stems, they provide storage and support– In roots, they store carbohydrates

Photosynthesis – Tissues Working Together

• Because sugar (glucose) is so important to all components of a plant, it must have a system in place to transport the sugars

• Oxygen is also required by plant cells (for cellular respiration)– Leaves produce more O2 than is needed,

and any excess is released as waste

Recall: Plants and Food

- Since plants cannot move like animals do to obtain food, they must make their own food through a process called photosynthesis.

light energy + carbon dioxide + water glucose + oxygen

glucose

Photosynthesis – Absorbing Light

light energy + carbon dioxide + water glucose + oxygen

• Leaves that are wide and thin are ideal for light absorption. Why?– Greater SA

Remember: Photosynthesis occurs in chloroplasts

Photosynthesis – Absorbing Light

• Chloroplasts are contained in the mesophyll layers– Palisade mesophyll is

located where there is maximum light

– Spongy mesophyll is located throughout leaf with air pockets in between

• Mesophyll layers as a whole are part of ground tissue system

Photosynthesis – Obtaining CO2

• CO2 will naturally diffuse into a leaf. To avoid too much diffusion, the leaf is coated with a layer of epidermal tissue called the cuticle

• Gases enter and exit through openings in the leaf called stomata

• Stomata are controlled by guard cells.

Photosynthesis – Obtaining Water• Leaves will close their

stomata when water levels are low

• Leaves obtain water through vascular tissues (xylem and phloem) – Arranged as bundles called

vascular bundles and run from root to leaf

– Root hairs (epidermal) grow into soil from roots and obtain water via diffusion

– Water is transferred via xylem, from the roots to the leaves

1. What is a tissue?2. Name the three tissue types in plants and briefly

describe their function.3. What is the difference between dermal and

periderm tissues?4. Describe the difference between the xylem and

phloem.5. What is the difference between the spongy and

palisade mesophyll?6. How does the shape of a leaf help photosynthesis

take place?7. What is a stomata? How do the guard cells open

and close?