Download session 4: plant tissues

Life Sciences
Grade 10
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SESSION 4: PLANT TISSUES
KEY CONCEPTS:
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Levels of Organisation
Definition of a tissue
Types of Plant Tissues
Plant Organs
- The Leaf
TERMINOLOGY:
Tissue a group of similar cells adapted for a particular function.
XPLANATION
TYPES OF PLANT TISSUES:
Meristematic Tissue:
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Cells of meristems divide continuously cells are similar in structure & have
thin cellulose cell walls may be spherical, oval, polygonal or rectangular in
shape contain few vacuoles
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Found in regions of the plant that grow, mainly at tip of root & stem. According
to their position in the plant, meristems are apical, lateral & intercalary.
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Simple Permanent Tissue:
Epidermis:
• Structure: Transparent, one cell thick and is usually covered with cuticle
usually has guard cells with stomata
• Found on the outermost layer of the plant body such as leaves, flowers, stem
& roots
• Function is to protect the plant from dessication and infection. Guard cells &
cuticle helps to reduce water loss
Parenchyma:
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Oval, round or elongated in shape.
Thin cell wall& encloses a dense cytoplasm which contains a small nucleus &
surrounds a large central vacuole.
Intercellular spaces are abundant.
WHERE?
• Soft parts of the plant - cortex of roots, ground tissues in stems & mesophyll of
leaves.
• Also - pith, medullary rays & packing tissue in xylem & phloem.
WHY?
• packing tissue
• support to the stem of herbaceous plants water & food storage transport of water
& gases
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Collenchyma:
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Characterised by the deposition of extra cellulose at the corners of the cells.
Intercellular spaces are generally absent.
WHERE?
• Mainly below the epidermis of dicotyledon stem & petiole.also occur in midribs
of dicot leaves.
WHY?
• Provides mechanical support & elasticity.
• Allows plant to bend without breaking.
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Transverse and Longitudinal Section of Collenchyma:
Scelerenchyma:
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Dead cells with no protoplasm.
The walls of cells greatly thickened & lignified.
Due to excessive thickening of the wall of sclerenchyma cells, its cell cavity or
lumen becomes nearly absent.
The cells of are closely packed.
No intercellular spaces.
WHERE?
• Stems, roots, veins of leaves, hard covering of seeds & nuts.
• Sclereids form the gritty part of the most of the ripe fruits & contribute
hardness to the seed coat & nutshells.
WHY?
• Mainly mechanical & protective in function.
• It gives strength, rigidity, flexibility & elasticity to the plant body
• Thus, enables it to withstand various strains.
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Sclereids / Stone Cells:
• Found flesh of fruit like pears.
• Also in pips of fruit and shells of nuts
Fibres:
• Make stems & roots tough & rigid
Complex Permanent Tissue:
tracheids
Xylem
vessel elements
Vascular
(Transport)
Tissue:
sieve-tube
elements
Phloem
companion cells
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Xylem:
Composed of cells of four different types:
• Tracheids, vessels, xylem parenchyma, xylem sclerenchyma.
• Except xylem parenchyma, all other xylem elements are dead & bounded by
thick lignified walls.
WHERE?
• Vascular bundles of roots, stems and leaves
WHY?
• Transport water & minerals salts upward from the root to different parts of
shoots.
• Since walls of tracheids, vessels & sclerenchyma of xylem are lignified, they
give mechanical strength to the plant body.
Components of Xylem:
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Vessels
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Tracheids
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Phloem:
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Composed of following:
1. Sieve Tubes
2. Companion Cells
3. Phloem Parenchyma
4. Phloem Fibres.
All phloem cells are living cells, besides fibres.
WHERE?
• Vascular bundles of roots, stems and leaves
WHY?
• Transport food materials from the leaves to the storage organs & later from
storage organs to the growing regions of the plant body
Sieve - Tube
Companion
Cells
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PLANT ORGANS:
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Organs:
Consist of a number of tissues that work together to perform a common overall
function.
Label the main plant organs:
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Leaves:
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Leaves - blade or lamina, an edge called the margin of the leaf, the veins
(vascular bundles), a petiole, and two appendages at the base of the petiole
called the stipules
Type of Leaves:
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Simple - blade not divided into smaller leaflets
Compound - blade divided into smaller leaflets
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Internal Structure:
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Guard Cells & Stoma:
Open:
Closed:
PHOTOSYNTHESIS
FUNCTIONS OF
LEAVES
GASEOUS
EXCHANGE
TRANSPIRATION
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X-AMPLE QUESTIONS:
Question 1:
Study the following diagram and answer the questions:
1.1 Provide labels for parts labelled A, D, E and G.
1.2 Part labelled C consists of parenchyma tissue. Explain how this tissue is suited
for its functions.
1.3 How do cells labelled B and C differ from ordinary parenchyma tissue?
1.4 Draw a fully labelled diagram to illustrate the structure of part labelled F.
1.5 List TWO functions of the leaf.
1.6 Explain how the leaf is suited to its functions.
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Question 2:
Identify each of the following tissues, provide ONE location, ONE function and ONE
structural suitability of each.
a)
b)
c)
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C
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