Plant Tissues & Anatomy

• A tissue is a group of similar cells working together to do one common function.
• The body order in plants is cell → tissue → organ (root, stem, leaf) → whole plant.
• Plants are fixed in one place, so they build internal equipment from cells: pipes, packing and support rods.
• The study of the internal structure of a plant is called anatomy.
• Plant tissues fall into two broad families: meristematic (dividing) and permanent (fixed-job) tissue.

A tissue is a group of similar cells working together to do one common function.

The study of the internal structure of a plant is called anatomy.

Plant tissues fall into two broad families: meristematic (dividing) and permanent (fixed-job) tissue.

• Early botanists grouped plants only by outward looks like flower colour and leaf shape.
• The deeper clue is whether a plant has vascular tissue (xylem and phloem).
• A. P. de Candolle (Swiss, ~1813) first classified plants by presence or absence of vascular tissue.
• He named two groups: Vasculares (with vascular bundles, e.g. ferns, seed plants).
• And Cellulares (without vascular bundles, e.g. algae, mosses).
• Later systems (Bentham & Hooker, Engler & Prantl) used many features; de Candolle was the first to use vascular tissue.

The deeper clue is whether a plant has vascular tissue (xylem and phloem).

A. P. de Candolle (Swiss, ~1813) first classified plants by presence or absence of vascular tissue.

He named two groups: Vasculares (with vascular bundles, e.g. ferns, seed plants).

And Cellulares (without vascular bundles, e.g. algae, mosses).

Later systems (Bentham & Hooker, Engler & Prantl) used many features; de Candolle was the first to use vascular tissue.

• Meristem = small, thin-walled cells that keep dividing to make new cells; the plant's cell factory.
• Plants grow only at special spots, not all over at once.
• Apical meristem sits at root tips and shoot tips and causes length-wise primary growth.
• Intercalary meristem lies between mature tissues (base of grass leaves) and regrows grazed/mown parts.
• Apical and intercalary are primary meristems; the sidelocated one is the secondary meristem.
• Lateral (secondary) meristem is cylindrical and causes thickness, i.e. secondary growth.
• An axillary bud is left in the leaf axil and can grow into a branch or flower.
• Apical — Root tip, shoot tip — Increases length (primary growth)
• Intercalary — Base of grass leaves/internodes — Regrows grazed/cut parts
• Lateral — Sides of stem & root — Increases thickness (secondary growth)

Meristem = small, thin-walled cells that keep dividing to make new cells; the plant's cell factory.

Apical meristem sits at root tips and shoot tips and causes length-wise primary growth.

Intercalary meristem lies between mature tissues (base of grass leaves) and regrows grazed/mown parts.

Apical and intercalary are primary meristems; the sidelocated one is the secondary meristem.

Lateral (secondary) meristem is cylindrical and causes thickness, i.e. secondary growth.

An axillary bud is left in the leaf axil and can grow into a branch or flower.

• The lateral meristem has two examples: vascular cambium and cork cambium.
• Vascular cambium sits between xylem and phloem.
• It makes new xylem on the inner side and new phloem on the outer side each year.
• This thickening produces the annual rings seen in a cut tree trunk.
• Cork cambium (phellogen) forms the protective bark (cork) on the outside of woody stems and roots.

The lateral meristem has two examples: vascular cambium and cork cambium.

Vascular cambium sits between xylem and phloem.

It makes new xylem on the inner side and new phloem on the outer side each year.

This thickening produces the annual rings seen in a cut tree trunk.

Cork cambium (phellogen) forms the protective bark (cork) on the outside of woody stems and roots.

• Permanent tissue = mature, specialised cells that have lost the ability to divide.
• They are the finished products of the plant's cell factory, each doing one fixed job for life.
• Simple permanent tissue = made of only one type of cell.
• Its three kinds are parenchyma, collenchyma and sclerenchyma.
• Complex permanent tissue = made of more than one type of cell cooperating.
• Its two kinds are xylem and phloem, which together form a vascular bundle.
• Memory trick: simple = single cell type, complex = combination of cell types.

Permanent tissue = mature, specialised cells that have lost the ability to divide.

Simple permanent tissue = made of only one type of cell.

Complex permanent tissue = made of more than one type of cell cooperating.

Its two kinds are xylem and phloem, which together form a vascular bundle.

• Parenchyma: living, thin cellulose walls, isodiametric; does photosynthesis, storage and secretion.
• It forms the bulk of cortex, pith and fleshy fruit parts.
• Chlorenchyma = parenchyma full of chloroplasts (green leaf mesophyll, does photosynthesis).
• Aerenchyma = parenchyma with big air spaces in water plants; helps them float.
• Collenchyma: living cells thickened at the corners with cellulose and pectin; gives flexible support (e.g. celery strings).
• Sclerenchyma: dead cells with thick lignified walls and narrow lumen; gives rigid strength.
• Sclerenchyma comes as long fibres (jute, hemp for rope) and stone-like sclereids (grit in pear).
• Exam tip: parenchyma and collenchyma are living; sclerenchyma is dead.
• Parenchyma — Living — Thin cellulose; storage, photosynthesis
• Collenchyma — Living — Corner-thickened; flexible support
• Sclerenchyma — Dead — Thick lignin; rigid strength

Parenchyma: living, thin cellulose walls, isodiametric; does photosynthesis, storage and secretion.

Chlorenchyma = parenchyma full of chloroplasts (green leaf mesophyll, does photosynthesis).

Aerenchyma = parenchyma with big air spaces in water plants; helps them float.

Collenchyma: living cells thickened at the corners with cellulose and pectin; gives flexible support (e.g. celery strings).

Sclerenchyma: dead cells with thick lignified walls and narrow lumen; gives rigid strength.

Sclerenchyma comes as long fibres (jute, hemp for rope) and stone-like sclereids (grit in pear).

• Xylem carries water and dissolved minerals upward from roots to stem and leaves.
• It also adds mechanical strength. Memory aid: in "X"ylem, water goes up.
• Xylem has four elements: tracheids, vessels, xylem fibres and xylem parenchyma.
• Tracheids: long, dead, lignified tubes with tapering ends; present in all higher plants.
• Vessels: wide, dead tubes with perforated end-walls for fast water flow; typical of angiosperms.
• Xylem fibres give support; xylem parenchyma (only living element) stores food.
• Three of the four xylem elements are dead; only xylem parenchyma is living.
• Tracheid — Dead — Conducts water
• Vessel — Dead — Conducts water fast
• Xylem fibre — Dead — Support
• Xylem parenchyma — Living — Food storage

Xylem carries water and dissolved minerals upward from roots to stem and leaves.

It also adds mechanical strength. Memory aid: in "X"ylem, water goes up.

Tracheids: long, dead, lignified tubes with tapering ends; present in all higher plants.

Vessels: wide, dead tubes with perforated end-walls for fast water flow; typical of angiosperms.

Xylem fibres give support; xylem parenchyma (only living element) stores food.

Three of the four xylem elements are dead; only xylem parenchyma is living.

• Phloem carries food (sugar made in leaves) to all parts of the plant; this transport is translocation.
• Food can move both up and down in the phloem, unlike one-way xylem.
• Phloem has four parts: sieve tubes, companion cells, phloem fibres and phloem parenchyma.
• Sieve tubes: living tube cells with sieve-plate ends that conduct food.
• Companion cells control the activity of sieve tubes.
• Phloem fibres are the only dead part of phloem; all other phloem cells are living.
• Carries — Water & minerals — Food (sugars)
• Direction — Upward only — Up and down
• Mostly — Dead cells — Living cells

Phloem carries food (sugar made in leaves) to all parts of the plant; this transport is translocation.

Food can move both up and down in the phloem, unlike one-way xylem.

Sieve tubes: living tube cells with sieve-plate ends that conduct food.

Companion cells control the activity of sieve tubes.

Phloem fibres are the only dead part of phloem; all other phloem cells are living.

• All plant tissues are grouped into three tissue systems.
• Epidermal (dermal) system: the outer protective layer with epidermis, stomata, root hairs.
• Stomata are tiny leaf pores guarded by guard cells for gas exchange and transpiration.
• Ground tissue system: all tissue except dermal and vascular; mainly parenchyma for storage and support.
• Vascular (conducting) system: the xylem and phloem bundles.
• A waxy waterproof layer called the cuticle covers the epidermis of aerial parts to cut water loss.

All plant tissues are grouped into three tissue systems.

Epidermal (dermal) system: the outer protective layer with epidermis, stomata, root hairs.

Stomata are tiny leaf pores guarded by guard cells for gas exchange and transpiration.

Ground tissue system: all tissue except dermal and vascular; mainly parenchyma for storage and support.

A waxy waterproof layer called the cuticle covers the epidermis of aerial parts to cut water loss.

• Vascular bundles are arranged differently in the two flowering-plant groups.
• In a dicot stem the bundles form a ring; in a monocot stem they are scattered.
• Dicot bundles are open (have cambium, so secondary growth occurs); monocot bundles are closed (no cambium).
• Annual rings and wood form only where cambium exists (mostly dicots and trees).
• Dicot leaves show reticulate (net) venation; monocot leaves show parallel venation.
• Bundle arrangement — Ring — Scattered
• Cambium — Present (open) — Absent (closed)
• Secondary growth — Yes — No

Vascular bundles are arranged differently in the two flowering-plant groups.

In a dicot stem the bundles form a ring; in a monocot stem they are scattered.

Dicot bundles are open (have cambium, so secondary growth occurs); monocot bundles are closed (no cambium).

Annual rings and wood form only where cambium exists (mostly dicots and trees).

Dicot leaves show reticulate (net) venation; monocot leaves show parallel venation.

• A stem bears nodes, internodes, buds and leaves; a root has none of these and bears root hairs.
• Ginger is a stem (rhizome), not a root, because it has nodes, scale leaves and buds.
• Stems carry water and minerals up (via xylem) and distribute food to all parts (via phloem).
• Underground stems: rhizome (ginger, turmeric), tuber (potato), bulb (onion), corm (colocasia).
• Buds are normally found in the leaf axil and at stem/shoot tips, confirming a structure is a stem.
• Stems also help in support, storage and (when green) photosynthesis.

A stem bears nodes, internodes, buds and leaves; a root has none of these and bears root hairs.

Underground stems: rhizome (ginger, turmeric), tuber (potato), bulb (onion), corm (colocasia).

Buds are normally found in the leaf axil and at stem/shoot tips, confirming a structure is a stem.

• In mango the part we eat is the fleshy mesocarp (the juicy middle layer of the fruit).
• Edible part of potato = stem tuber; ginger = rhizome (stem); onion = bulb (modified leaves).
• Edible part of carrot and radish = root; cabbage = leaves; cauliflower = flower.
• Edible part of apple and pear = swollen fleshy thalamus (false fruit), with gritty sclereids in pear.
• These food and fleshy stores are mostly parenchyma tissue.
• Mango — Mesocarp (fruit pulp)
• Potato — Stem tuber
• Ginger — Rhizome (stem)
• Carrot/Radish — Root
• Onion — Bulb (leaves)

In mango the part we eat is the fleshy mesocarp (the juicy middle layer of the fruit).

Edible part of potato = stem tuber; ginger = rhizome (stem); onion = bulb (modified leaves).

Edible part of carrot and radish = root; cabbage = leaves; cauliflower = flower.

Edible part of apple and pear = swollen fleshy thalamus (false fruit), with gritty sclereids in pear.

These food and fleshy stores are mostly parenchyma tissue.