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?