Biology - Chapter 23: Structure of Flowering Plants

tap roots (primary root)

• one main root that comes from radicle of the seed

• lateral & secondary roots emerge from this

• tips of the lateral roots have thousands of tiny, invisible root hairs

• present in most dicots

• e.g. carrots

radicle

the initial root that emerged from the seed

fibrous roots

• formed when the radicle dies away to leave a group of equal-sized roots from the base of the stem

• common in monocots

• e.g. grass

adventitious roots

• roots that don’t develop from the radical & are found in strange places

• e.g fibrous roots & gripping roots of ivy, onion roots

functions of the root

• anchors plant in soil for stability

• absorbs water and mineral salts from soil - root hairs carry out this function

• transport absorbed substances to the shoot

• some roots store food, e.g. carrots, turnips, radishes

the zones in a root

1. Zone of protection

2. merismatic zone (zone of cell production)

3. zone of elongation

4. zone of differentiation

1. Zone of Protection

• root cap protects root cells as they push through the soil

2. Merismetic Zone

• has meristems that can divide and allow plants to grow

• apical meristems → found at root tip and in shoot tip

• lateral meristems → along side of plant

• cells in the root meristem are constantly dividing by mitosis to produce new cells for root growth

3. Zone of Elongation

• when the meristem form new, very small cells, plant growth regulators(hormones) such as auxins in this zone stimulate the cells to grow longer

4. Zone of Differentiation

elongated cells (which are all similar/undifferentiated) develop into different tissues:

• dermal tissue - surrounds and protects plant (e.g. epidermis)

• vascular tissue - transports minerals and water around the plant (e.g. xylem & phloem)

• ground tissue - found between dermal and vascular tissue

stems

• main part of the shoot

• stem carries leaves which emerge through nodes

• internode is between the 2 notes of the stem

• apical bud/lateral buds are located along the stem

• lenticels are found on stems & are openings for gas exchange (white dots on stem)

herbaceous plants

don’t contain woodd/lignin

node

the point on a stem at which a leaf is attached

internode

the point between 2 nodes

bud

a potential growth point that may develop into a shoot, leaf or flower

functions of stems

• support aerial parts of plants

• transports water and minerals from the roots to the leaves and flowers

• transports food made in the leaves to the roots

• carry out photosynthesis when they are green

• may store food (e.g celery)

axil

the angle between a leaf & stem → auxiliary or lateral buds are located at each axil

venation

the pattern of a leaf

leaf structure

• leaves are attached to stems a nodes

• petiole → stalk of the leaf

• some leaves don’t have petioles: sessile leaves

• leaf is normally flattened into a thin leaf blade of lamina

• petiole continues through lamina as the midrib

• veins emerge from the midrib & the veins containvascular or transport tissue like xylem or phloem

parallel venation

• veins run alongside each other

• found in most monocots, e.g. grass

net/reticulate venation

• veins from a branching network throughout the lamina

• common in dicots, e.g. rose, buttercup

functions of leaves

• photosynthesis

• gas exchange in stomata with atmosphere

• transpiration → water loss

• food storage

dermal tissue

• the skin of a plant → called the epidermis & protects plant

• epidermal cells are living, rectangular cells

• function: protect the cells

ground tissue

• occupies the area between the dermal & vascular tissue in a plant

• makes up most of the bulk of the young plant

• range of functions such as photosynthesis & storage

vascular tissue

for transportation of materials: xylem & phloem

xylem

appearance: xylem tracheids & xylem vessels

function: transports water & mineral salts from root to leaves + gives mechanical support to plant due to lignen

location: found in vascular bundles (special groups of transporting cells)

xylem tracheid

• long, sloping or tapering cells whose insides are hollow and at maturity

• they overlap & pits in the walls allow water and minerals to pass sideways from cell to cell

• walls thickened with lignen for support

xylem vessel

• elongated, tubular structures formed when number of cells join end-to-end

• spiral lignin for strength

• has no end walls - forms a continuous tube

• pits to allow sideways movement of water

phloem

mainly composed of sieve tunes & companion cells

function: sieve tubes transport food made by photosynthesis from leaves to the rest of the plant + companion cells control the activities of the sieve tube elements

location: found in roots, stems, leaves and flowers

cotyledons

first leaf that develops in a seed

monocots

• single cotyledon

• long, narrow leaf

• parallel venation

• mostly herbaceous plants

• scattered vascular bundles

• flowering parts in multiples of three; e.g. 3, 6 or 9 petals in a flower

dicots

• 2 cotyledons

• may be herbaceous or woody

• broad & reticulate venation

• vascular bundles arranged in a ring

• flower parts in multiples of 4 or 5