Plants pt 1

Leaves

Organs where photosynthesis take place

Where are leaves located

At nodes along the stem

petiole

Stalk which connects leaf to stem

2 types of leaves

Compound and simple

Simple leaves

No leaflets

Compound leaves

2+ leaflets

Adaptations of leaves (7)

1. Broad leaflets to trap more sunlight in shady areas
2. Evergreen needles to reduce water loss (can’t freeze in the narrow column)
3. Though, bitter or prickly leaves to discourage hungry herbivores
4. Toxin production as a natural insecticide
5. Tendrils to attach to surfaces (Eg beans and ivy)
6. Bulbs (Eg onions) for water and nutrient storage
7. Attractive petals to attract pollinators

Non-vascular plants + example

Don’t have vessels for transport

Eg mosses

Vascular plants

Tracheophytes - Have conducting tissues to transport water and carbs throughout plants

Gymnosperms

“Naked seed” plants e.g. conifers

Angiosperms

“Enclosed seeds” flowering plants e.g. tomatoes

Vascular systems

1. Shoots (above soil line)
2. Roots (below soil line)

Tissues

Group of cells working together to carry out a specific function

main plant tissue groups

1. Vascular tissue
2. Ground tissue
3. Dermal tissue
4. Meristematic tissue

Vascular tissue

Occurs in strands

Continuous from root to leaf

Types of vascular tissue

Xylem and phloem

Xylem

Conduct water and suspended minerals from roots to plant

Consists of dead cells at maturity

Phloem

Vascular tissue which transports water and dissolved sugars (carbs) from leaves to roots, shoots or fruits

Consists of living cells at maturity

Ground tissue

Surrounds vascular tissue

Types of ground tissue

Parenchyma, collenchyma and sclerenchyma

Parenchyma

Living, spherical, thin-walled cells

Photosynthesize and store nutrients/water

E.g. Apple flesh, potatoes, radishes

Sclerenchyma

Dead, thick-walled cells (very rigid) with cellulose and lignin

Strengthen support and protect plant

E.g. nut shells

Collenchyma

Living, thick-walled cells

Strengthen and support plant

E.g. celery stalk

Types of dermal tissue

Epidermis and periderm

Epidermis

Dermal tissue that is the outer protective layer of leaves, stems and roots

Usually only one cell thick

Periderm + example

Dermal tissue that protects inner tissues from injury

Replaces epidermis in later growth

Cells are dead at maturity

E.g. cork

Meristematic tissues

Produces new cells by mitosis - undifferentiated

Types of meristematic tissue

Apical and lateral

Apical tissue

Meristematic tissue at root and shoot tip

Responsible for primary growth- lengthens roots and shoots

Lateral tissue

Aka cambium

Meristematic tissue responsible for secondary growth to increase root and shoot diameter

Stems divisions

Nodes and internodes

Nodes

Hold buds

Buds

grow into leaves, flowers, cones or other stems

Internodes

Distance between nodes on stems

Functions of stems

Support

Transport link between root and rest of plant

Storage of nutrients

Types of stems

Woody

Herbaceous

Woody stems

* thick, rough, long-lived
* Capable of supporting great heights
* Undergo secondary growth in xylem (new wood increases stem diameter each year)
* Make cork cells from cork cambium
* Surrounded by bark
* Composed of heartwood
* Composed of sapwood

E.g. oak trees, conifers, shrubs

Bark

Tissue from cambium outward in woody stems

Heartwood

Darker , older, dead xylem which makes up woody stems along with sapwood

Sapwood

Lighter, younger, living xylem which makes up woody stems along with heartwood

Herbaceous stems

Thin, soft, short-lived

Usually short (expedition: palm trees)

Types of herbaceous stems

Monocot and dicot

Monocot stems

Herbaceous stems with:

* scattered vascular bundles
* 2 distinct parts (xylem and phloem)
* No bark, annual rings or wood

E.g. corn stem

Dicot stems

Herbaceous stems which have:

* vascular bundles in a circular arrangement
* 3 distinct parts - xylem, phloem, cambium

E.g. bean stem

Functions of roots

1. Anchor plant to soil
2. Absorb water, nutrients, and minerals from soil/growth medium
3. Store food/carbs
4. Produce hormones
5. Propagate/reproduce/grow a new plant

Types of roots

Primary and secondary/lateral

Primary roots

First root to develop from seed

Secondary/lateral root

Branches from primary root

types of roots in different plants

Tap, fibrous, adventitious

Tap root

Single deep root that stores food and obtains deep ground water

E.g. carrots, beets, radishes, dandelions, oak trees

Fibrous roots

Many branched roots which absorb surface water quickly

E.g. grasses, rye

Adventitious roots

Grow from plant shoots and eventually form a fibrous root system

E.g. climbing aerial roots of ivy and prop roots of mangrove trees

Root hairs

Small, hair-like extensions of root epidermal cells which increase surface are for water absorption

How water gets from roots to plant

Enters root hairs - cortex - phloem - xylem

Root pressure pushes water up the roots xylem

How water is transported in the xylem (root to leaf) steps

\
Osmosis

Transpiration

Root pressure

Adhesion

Cohesion

How water is transported by the xylem: osmosis

Water enters the root across the semi-permeable membrane by osmosis

How water is transported by the xylem: transpiration

Water is lost in leaves through evaporation through the stomata which pulls other molecules to replace them

How water is transported by the xylem: root pressure

Plant roots build up pressure that worked water upwards into the plant

Adhesion

water molecules are attracted to xylem vessels (capillary action)

The narrower the tube, the higher the water climbs

How water is transported by the xylem: cohesion

Attraction of water molecules to e/o

How sugars is transported by the phloem

Sugars are translocated through sieve-tube elements in the phloem in more then 1 direction (upward, downward, sideways) simultaneously

Pressure flow hypothesis/mass flow theory

Relies on combination of osmosis and pressure differences between source cells and sink cells

Source cells

High sugar cells (Eg leaf cells)

Sink cells

Low sugar cells (eg root cells)

How water is transported by the xylem: steps

\
Leaf produces sugar

Sugar enters sieve tube of phloem

H2O enters phloem from nearby cells

Pressure inside phloem increases

Contents of elements are pushed from cell to cell

Blade

Thin, flattened, main portion of the leaf

Petiole

An extension which joins the blade to the stem

Lateral bud

Young inactive shoot that will eventually grow into a new branch

Located above where the leaf attaches to the stem

Shoot apex

Upper portion of a stem where growth occurs

Shoot system

part of the plant located above ground

Types of cells in xylem

Tracheids

Vessel elements

Tracheids

Long, narrow, overlapping cells located in the xylem with pits to transport H2O

Vessel elements

Xylem cells with thickened walls and large pores

Types of cells in the phloem

Companion cells

Sieve plate

Companion cells

Nucleated cells in the phloem tissue which carry out the cell functions of the adjacent sieve cells

Sieve cells

make up the sieve plate which has large pores for passage of material

Cuticle

Waxy layer on top of epidermis

Prevents water loss

Palisade mesophyll cell

Site of most photosynthesis

Vascular bundle

‘Vein’ of leaf

Spongy mesophyll cell

Site of some photosynthesis

Air spaces between these cells allow for gas exchange

Guard cell

Controls opening of stomafor gas exchange

Stoma/stomate

Pore which opens and closes for gas exchange on underside of leaf

T/F - all epidermal cells contain chloroplasts

F - guard cells around the stomate are the only épidermal cells containing chloroplasts

How does the stomate open

Dawn: photosynthesis begins in the guard cells. sugar accumulates and water concentration decreases

Water from surrounding cells diffuses onto the guard cell by osmosis causing them to swell and curve

Now curved, the stomate to open and CO2 to enter the leaf

Process of stomate closing

Sunset: photosynthesis stops but respiration continues causing sugar to build up in surrounding cells

Water exist the guard cells by osmosis and the guard cells become limp and wilted

Once wilted, the thick wall closes and the stomate straightens and closes

Thick and thin walls of the stomate

Thick inner wall and thin outer wall

Transpiration

Loss of water from leaves by evaporation

Caused by opening and closing of stoma

Inner root layer

Transport/vascular tissue

Middle layer of root

Store water and food for the root

Outer root layer

Contains root hairs

Root cap

Protects a root tip from damage as it grows into the soil

Make of dead cells

What materials are carried up from roots by vascular tissue

Water + dissolved nutrients

What material do vascular tissue carry down to roots from leaves

Glucose (food)

New root growth mainly occurs from the _____

Tip

Most water enters a plant through the _____

Root hairs

Meristem

Undifferentiated cells that give rise to new cells at the bottom of a root

Region of maturation

Location of root where cells specialize into other types of tissues

Region of elongation

Region open root where cells increase in length to push root deeper into soil

Epidermal

Xylem