Chp 23 + 24

Is the shoot system above or below ground?

above

Is the root system above or below ground?

below

Tap roots

• primary root grows from the radicle
• lateral/fibrous/secondary roots are formed from the primary root, and have tiny hairs on them
• present in most dicots

Tap root: example

carrot

Fibrous roots

• form when the radicle dies
• equal sized roots emerge from the base of the stem
• most common in monocots

Fibrous roots: example

grass, daffodils

Adventitious roots

• do not develop from a radicle
• grow in strange places

Adventitious roots: example

roots at the base of an onion

Function of Roots

• anchor the plant
• absorbs water and minerals from the soil, through the root hairs
• transports materials to the shoot
• store food

What are the 4 zones in a root?

• zone of protection
• zone of cell production/meristematic zone
• zone of elongation
• zone of differentiation

Zone of protection

the root cap protects the root as it pushes through the soil

Zone of cell production/Meristematic zone

• apical meristems are found here
• constantly undergoing mitosis to produce new cells so the roots can grow

Meristem

plant tissue that is capable of mitosis

Zone of elongation

• the new cells formed by the meristem are very small and need to grow
• plant growth regulators such as auxin stimulate the cells to grow larger

Zone of differentiation

elongated cells are specialised and divided into 3 different types of tissues

Herbaceous plant

• usually soft and green
• does not contain lignin

Woody plant

• hard and woody
• does contain lignin

Stem structure: nodes, internodes, apical bud, axial, auxilliary/lateral buds, lenticel

nodes - where leaves and branches emerge from the stem
internodes - part between nodes
apical bud - the tip of the stem which is responsible for plant growth
axial - the angle between the leaf and the stem
auxilliary/lateral buds - found at each axial, responsible for the growth of new leaves or branches
lenticel - opening found in the stems that allows gas exchange to occur

Functions of the stem

• supports aerial parts of the plant
• transports water and minerals from roots to leaves
• transports foot from leaves to roots
• carries out photosynthesis
• store food

Example of a stem adapted to store food

Potato tuber

Leaf structure: petiole, lamina, midrib, veins

petiole - the stalk of the leaf, contains transport tissues
lamina - thin flat blade structures, aka the leaves
midrib - petiole continues through the lamina, contains transport tissues
veins - contains transport tissues

Venation

The pattern vein in a leaf

Parallel venation + Example

• the veins run along side each other
• grass, daffodils

Net/reticulate venation + Example

• veins form a branching structure throughout the leaf
• roses

Functions of leaves

• make food by photosynthesis
• exchange gases with atmosphere
• lose water by transpiration
• store food

Example of a plant adapted to store food in the leaves

Spinach

3 types of plant tissue

• dermal tissue
• ground tissue
• vascular tissue

Dermal tissue + Function

• outer layer of the plant (epidermis) protects the plant
• some plants have a waxy cuticle which prevents water loss in hot climates

Ground tissue + Function

• cortex is the area occupied by the ground tissue
• makes up the bulk of the plant
• carries out photosynthesis, provides strength and support to aerial parts of the plant, stores food (only some plants)

Vascular tissue + Function

• made up of the xylem and phloem, contained in vascular bundles
• xylem transports water and minerals
• phloem transports food

Structure of xylem

• consists of tracheids and vessels

Is xylem living or dead?

considered a dead tissue as the living contents die before maturity

Function of xylem

• responsible for the transport of water from the roots to the leaves
• spiral lignin provides support for the plant

Location of xylem

• found in the roots, stem, leaves, flowers
• found in vascular bundles

Tracheids

• long, tapered, hollow cells
• overlap and allow water to pass from one to the other through tiny slits called pits

Vessels

Tubular structures - a number of cells join end to end, the end wall is broken down to form a continuous tube
Pits - allows water to pass from side to side

• more efficient than tracheids due to being wider and continuous tubes

Structure of phloem

made up of sieve tubes and companion cells

Function of Phloem

transports food made by photosynthesis form the leaves to the rest of the plant

Location of phloem

• found in roots, stems, leaves
• found in vascular bundles

Sieve tubes - structure

Sieve tube elements - individual elements that are long tubular structures joined on top of eachother, they contain cytoplasm but do not have a nucleus
Sieve plates - end walls that contain pores to allow the passage of materials from one element to another
Cell wall - made of cellulose and no lignin is present

Companion cells

• for every sieve tube there is a companion cell
• contains a nucleus and a dense cytoplasm
• control the activity of the sieve tube

Is phloem living or dead?

living due to the presence of the companion cell, and its nucleus

Transverse section of a root diagram

Longitutindal section of a root diagram

Transverse section of a monocot stem diagram

Transverse section of a dicot stem diagram

Longitudinal section of a monocot stem diagram

Longitudinal section of a dicot stem diagram

Longitudinal tracheid diagram

Longitudinal vessel diagram

Longitudinal phloem diagram

Transverse phloem diagram

Characteristics of a Monocotyledon

• contain 1 seed leaf
• mostly herbaceous, soft and not woody
• parallel venation
• vascular bundles are placed at random along the stem
• flowering plants are arranged in multiples of 3
• eg daffodils, grasses

Cotyledon

a leaf in the seed specialised for food storage

Characteristics of a Dicotyledon

• contain 2 seed leaves
• herbaceous or woody
• broad leaves with net venation
• vascular bundles arranged in rings
• petal arrangement in multiples of fours or fives

Differences between Monocots + Dicots

How is water taken up by the roots?

• water diffuses into the root hairs

• they are well adapted for this as they have thin walls, a large surface area and no cuticle

• the cytoplasm of the root cells is more concentrated with salts and sugars, so the water moves in from the soil

• water diffuses from the root hairs across an area called the cortex, which is the area occupied by ground tissue, and into the xylem tissue

How does water move upwards in the plant?

1. Root pressure

• the build up of water in the roots causes pressure to build called root pressure

2. Transpiration - the cohesion tension model

• water evaporates into air spaces

• transpiration pulls each water molecule out of the xylem and the next water molecule is pulled with it due to high cohesion

• This give water the ability to be pulled up only works in narrow tubes such as the xylem

• the pulling of the water molecules causes the xylem to stretch and puts the water under tension, causing the xylem to become narrower

• at night when the stomata close, transpiration stops and the lack of tension returns the xylem to their original shape

Transpiration

the loss of water vapour from the leaves and other aerial parts of a plant by evaporation

Where does transpiration occur?

the stomata found on the underside of the leaf

What happens when a plant loses too much water?

• the plant wilts - it has lost more than their weight in water

  • is they do not replace the water they may die as the cells are less turgid and cannot stand strong

How do plants control the loss of water?

1. Waxy cuticle

• usually on the upper surface exposed to more sunlight, prevents excess water from evaporating as it cannot pass through

2. Stomata

• are located on the lower surface to prevent water loss as they receive less sun exposure, and have a lower rate of transpiration

3. Guard cells

• 2 guard cells on each stomata regulate the opening and closing of the stomata, depending on environmental conditions

Who proposed the cohesion-tension model?

Dixon + Joly

Cohesion

the ability of the same molecules to stick together

Adhesion

the ability of different molecules to stick together, but this foce is not as great as cohesive forces

Name 2 minerals absorbed through the roots?

calcium + magnesium

How do minerals enter the roots?

active transport, energy is supplied by mitochondria in the root hairs

In what type of cell does photosynthesis occur?

mesophyll cells

How does a plant get CO₂?

• comes throught the stomata from the atmosphere into air spaces

  • produces by the leaf in respiration

Leaf Structure diagram

Where are chloroplasts found within the leaf tissue?

ground of mesophyll

How are the products of photosynthesis used by the plant?

Glucose - either used immediately of converted and stored as starch

Sucrose - some glucose is converted to sucrose and enters the phloem

the sugary water solution is called phloem sap

Name a root modified for storage

carrot

Name a stem modified for storage

potato tuber

Name a leaf modified for storage

onion

Briefly describe gas exchange in the leaves

CO₂ - higher level of CO₂ in the atmosphere, diffuses into mesophyll cells through the air spaces

O₂ - photosynthesis produces oxygen which diffuses through the meosphyll cells into the air spaces and out the stomata

Water vapour - diffuses through the stomata

What factor controls the opening and closing of guard cells?

carbon dioxide

stomata will also close in high temperature to minimise water loss

Describe how the guard cells open and close the stomata:

• when guard cells absorb water and swell, they buckle outwards due to their thick cell wall, opening the stomata

• when guard cells lose water they become flaccid and shrink, causing the gap to close

How do CO₂ levels control stomatal opening and closing?

• high levels causes stomata to close

• usually closed at night as there is no photosynthesis but there is respiration

• low levels cause stomata to open

• usually open during the day as photosynthesis is occurring and using up CO₂, stomata open to allow more CO₂ in