Biology: Plants

Photosynthesis

* A series of chemical reactions that converts energy from sunlight into chemical energy stored in molecules
* Permits life
* Although plants use some of the oxygen molecules that they produce for cellular respiration, most of the oxygen is released into the atmosphere

Plant Systems

1. Roots (underground)
* Made up of roots
2. Shoots (above-ground)
* Made up of leaves and stems

Root Functions

* Anchors
* Transports water and minerals
* Absorbs water and minerals
* In some plants they store food, such as starches

Shoot Functions

* Supports
* Holds leaves up for photosynthesis
* Acts a highways to transport water, minerals and food

Plant Cell

* Plants contain:
* A cell wall, which provides support to the plant
* A large central vacuole
* Chloroplasts, which are used to carry out photosynthesis

Types of Plant Cells

* Parenchyma tissue
* Collenchyma tissue)
* Sclerenchyma tissue

Parenchyma Cell

* Flexible, thin-walled cells
* **Alive** at maturity


* Make up most of the cells throughout a plant
* The basis for many plant structures


* These cells are spherical in shape
* Their cell walls flatten when packed tightly together
* When found in leaves and green stems, they have many chloroplasts, which produce glucose by carrying out photosynthesis
* Other parenchyma cells, such as those found in roots and fruits, lack chloroplasts but have large entral vacuoles that store substances (such as starch, water, or oils)

Parenchyma Cell **Functions**

* Storage
* Photosynthesis
* Gas exchange
* Protection

Collenchyma Cell

* Often elongated and occur in long strands or cylinders that provide support for the surrounding cells
* **Alive** at maturity


* Make up the pull-apart strings in celery
* Can have unevenly thickened cell walls
* As a collenchyma cell grows, the thinner portions of its cell wall can expand
* This growth pattern makes them flexible and allows plants to bend without breaking

Collenchyma Cell **Functions**

* Supports surrounding tissues
* Provides flexibility for the plant
* Tissue repairs and replacements

Sclerenchyma Cell

* Have very thick secondary cell walls that contain **lignin**
* **Dead at maturity**
* Lacks cytoplasm and other living components when they mature, but their thick, rigid cell walls remain

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* Two types of sclerenchyma cells:
* **Sclereids**
* Also called stone cells
* Distributed randomly throughout the plant
* Shorter than fibre cells and have an irregular shape
* Responsible for the gritty texture of pears and the hard covering of seed coats
* **Fibres**
* Needle-shaped and have thick cell walls and small interior spaces
* When they are stacked end-to-end, fibres from a tough elastic tissue

Lignin

* A strong substance that makes the cell walls very tough and hard

**Primary Function** of Sclerenchyma Cell

* Provides support for **mature** plants

Four Main Plant Tissues

* Meristematic tissue
* Dermal Tissue
* Ground Tissue
* Vascular Tissue

Meristematic Tissue

* Undifferentiated embryonic plant tissue from which all other plant tissues develop
* Areas made up of meristematic tissue, or rapidly dividing cells through mitosis, are called *meristems*
* Has **primary** and **secondary** growth

Primary Growth

* Plants that are limited to this stage are called herbaceous
* Shorter, weaker
* The tips of a plant’s root and stems are constantly growing longer due to the division of cells in the ***apical meristem***
* ***Intercalary meristems*** are tissues found along the stems and at the base of the leaf blades of some vascular plants
* The cells produced from these types of meristems cause roots, stems and leaves to grow **longer** throughout the life of the plant
* If grasses had no intercalary meristems, they would stop growing after they were first mowed

Secondary Growth

* These meristems add vascular tissue, strengthens the stem, and provides support as the plant grows taller
* Allows them to grow **taller** and **wider**
* An increase in the circumference (girth) of roots and stems results from the division of cells in two types of ***lateral meristems***
* Vascular cambium
* Cork cambium

Vascular Cambium

* A thin layer of meristematic tissue that can run along the length of roots and stems and provides new vascular tissue
* Necessary for secondary growth

Cork Cambium

* Produces cells that develop tough cell walls and form a protective layer on the outside of stems and roots
* Makes up the outer bark on woody plants

Dermal Tissue

* Outer covering of a plant is made up of dermal tissue
* Protects the plant and prevents water loss
* The epidermis is a single layer of dermal tissue cells that forms a protective covering over the body of non-woody (herbaceous) plants and young woody plants
* Older woody plants form dermal tissue called **periderm**, which is a part of **secondary growth**
* Replaces the epidermis to form cork in woody stems and roots

Specialized Epidermal Tissue

* Guard Cells
* Trichomes
* Root Hairs

Guard Cells

* **Majority are located on the underside of the leaf**
* Paired cells that surround a stoma
* They control the size of the stoma
* When stomata are open, gas exchange can occur
* During the day, carbon dioxide diffuses in through the stomata and oxygen diffuses out
* Water in the form of gaseous water vapour also diffuses out of the plant and into the atmosphere through stomata
* Guard cells are there to prevent stomata from being constantly open, otherwise too much water would escape the plant

Stomata

* A small opening, usually in the leaf, that allows gas exchange to occur
* **Majority are located on the underside of the leaf**

Trichomes

* Tiny growths on the surface of the epidermis
* Often found on stems and leaves, and can make the plant appear fuzzy or woolly
* Keeps leaf surfaces cool and reduces evaporation
* Some may secrete sticky or toxic substances that repel herbivores

Root Hairs

* Tiny extensions of individual epidermal cells on plant roots
* Increase the surface area available for the absorption of water and nutrients

Ground Tissue

* Forms most of the plant’s internal and external material
* Contains parenchyma, collenchyma, and sclerenchyma cells
* They photosynthesize, store, and support
* Provides support for the plant when it grows between other types of tissues

Vascular Tissue

* Internal system of tubes that run lengthwise throughout the stem of a plant, connecting the roots and the leaves
* Transports water and dissolved substances throughout the plant
* Two types:
* Xylem
* Phloem
* Organized into **vascular bundles**
* Are scattered throughout the stem in monocots
* Arranged in rings in dicots

Xylem

* Transports water and minerals from the roots to the leaves
* In **gymnosperms**, xylem consists of cells called ***tracheids***


* In **angiosperms**, it consists of: **tracheids** and ***vessel elements***
* They both begin as living cells growing end to end in an immature stem
* When they mature, their living contents die, leaving the non-liviing cell walls in place
* Fluids are passed from one tracheid or vessel element to the next through pores (known as pits)

Phloem

* Food-conducting tissue in vascular plants
* Two types of pholem cells: ***sieve tube elements*** and ***companion cells***
* Both of these are alive at maturiy

Sieve Tube Elements

* Have no nuclei
* Have plates at both ends that are perforated with holes, making them resemble a sieve
* Each has an associated companion cell that does have a nucleus
* Acts like a valve since it controls the glucose in phloem since it moves up *and* down

Plant Organs

* Roots
* Leaves
* Stems

Main Divisions of Vascular Plants

* Gymnosperms
* Angiosperms

Gymnosperms

* Non-flowering plants
* Seeds are **not** enclosed
* Seeds of these plants are often carried in cones
* Subcategory includes conifers

Angiosperms

* Flowering plants
* Can be further subdivided into two categories:
* Monocots
* Dicots

Seed Contents

* Seed coat
* Endosperm
* Embryo

Cotyledon

Seed leaf

Monocots

* One cotyledon
* Usually three floral parts (or multiples of three)
* Usually a parallel array of leaf veins
* One pore of furrow in pollen grain
* Vascular bundles scattered in the stem

Dicots

* Two cotyledons (part of the embryo)
* Usually four or five floral parts (or their multiples)
* Usually a netlike array of leaf veins
* Three pores of furrows in pollen grain
* Vascular bundles arrayed as a ring in stem

Outer Root Layers

* Root hairs cover the outer surface
* Contains cortex and endodermis

Cortex

* Inside of the epidermis
* Made of ground tissue
* Pushes water and nutrients absorbed into vascular bundles so they can be distributed throughout the plant

Endodermis

* Allows water and nutrients to pass into vascular tissue
* Outer part of the cortex

Inner Root Layers

* Center of the root contains xylem and phloem
* Monocots form a ring around a central core surrounded by phloem
* Dicots form an X shape with phloem between

Types of Roots

* Taproots (dicots)
* Fibrous roots (monocots)
* Aerenchyma roots are found in aquatic plants

Stems

* Act to hold up leaves to the light so the cells can perform photosynthesis
* Act as highways, allowing water, minerals and food to be transported around
* Two types:
* Herbaceous: non-woody; die in the water (eg. flowers)
* Woody: covered in wood; stay alive in the winter (eg. trees)

Stem Modifications

* Includes:
* Development of bulbs
* **Rhizomes** which connect two plants underground

Leaves

* Main function is to carry out photosynthesis
* Epidermal cells of leaves secrete a waxy substance called a **cuticle**
* Contains mesophyll

Mesophyll

* Found in leaves
* Contains numerous chloroplasts
* Two types:
* Palisade mesophyll
* Spongy mesophyll

Palisade Mesophyll

* Where photosynthesis takes place
* On the top side of the leaf
* Dense + closely packed to maximise light absorption

Spongy Mesophyll

* Irregular-shaped palenchyma cells with open air spaces
* On the underside of the leaf because it needs good air flow for the gas exchange that occurs with stomata

Leaf Identification

* Leaf type
* Leaf venation
* Leaf arrangement

Leaf Type

* Simple leaf
* Has one leaf on the stem
* Compound leaf
* Has multiple leaves on the same stem

Leaf Venation

* Parallel venation (straight lines top to bottom)
* Pinnately netted (typical leaf, lines come from the center *line*)
* Palmately netted (comes from a *center point*; like a palm tree or fan)

Leaf Arrangement

* Basal (one leaf per stem + multiple stems)
* Opposite (two leaves on opposite sides growing from the same point on the stem)
* Whorled (like a flower; leaves make a circle shape around the point that they grow from)
* Alternate (leaves alternate sides like *-*-_ , + imagine a stem between those lines)

How is water lost from leaves?

Through transpiration and evaporation

Transport in Plants

* Soil into roots
* Roots into stem
* Stem into leaves

1. Transport in Roots

* H2O enters roots from soil through osmosis
* Nutrients enter through active transport, which requires energy
* Root hairs have greater osmotic potential than soil
* Root cells use ATP to actively pump ions into cells
* High concentration of ions creates a greater osmotic pressure in plant than surroundeing soil water; water moves into cells by osmosis
* Casparian strips block water movement; they force water through cell membranes of endodern
* Endodermal cells select nutrients that enter xylem

Osmotic Potential

* Pressure that must be applied to stop osmosis
* The potential of water to move from the region of its higher concentration to the region of its lower concentration

Casparian Strip

* Semi-permeable to allow only certain substances to enter the plant

2. Transport in Stems

* Root pressure is created by incoming nutrients + water
* Water molecules have an adhesive and cohesive property due to their polarity
* They form bonds with only another, which creates a chain
* This chain is adhesive, allowing them to stick to the sides of the xylem walls, thereby allowing them to travel *upwards*

Transport in Xylem

* Only moves upwards
* Xylem includes **2** types of dead, hollow, tubular cells:
* Vessel members (slightly larger diameter; cells stacked)
* Tracheids (smaller diameter; side to side overlap)
* Gymnosperms contain tracheids, whereas angiosperms contain tracheids and vessel members
* Water molecules sticks to walls of xylem (adhesion) and to each other (cohesion)
* Water moves through xylem in unbroken columns
* Air on leaf surfaces causes water to evaporate, creating a ‘pull’ on the water column

Turgor Pressure

* Water pressure in plant


* When there is a lot of water, the cell becomes **turgid** and the vacuole swells + pushes against the cell wall
* When there is not a lot of water, the cell becomes **flaccid** and the vacuole shrinks (cell loses its shape)

Transpiration

* Process of evaporative water loss in plants

Transpiration vs Evaporation

* Transpiration makes the surface of leaves and young stems wet and protects them from sunburn
* Evaporation provides dryness to the free surface

Transport in Phloem

* Only sugars are transported
* Direction is up *and* down

3. Transport in Leaves

* H2O is evaporated from leaves, called transpiration
* Due to H2o attraction, as H2O molecules leave through the stomata, water is pulled up the stem

Asexual Reproduction

* Parents produce genetically **identical** offspring
* New individuals can be grown from a portion of the roots, stems, or leaves of a parent plant
* Called artificial propagation

Artificial Propagation

1. Splitting
2. Leaf Cutting
3. Stem Cutting
4. Tissue Culturing

Splitting

* Method of artificial propagation
* To take a large chunk of roots or stems, gently tug them apart and replant them at two parts

Leaf Cutting

* Method of artificial propagation
* To cut across the leaf and replant it in new potted soil
* Especially where meristematic tissue develops roots

Stem Cutting

* Method of artificial propagation
* To cut the stem at an angle to expose it, let it grow on its own in water, and then let the roots emerge and plant it into soil

Tissue Culturing

* Method of artificial propagation
* To shave off pieces of the plant cell and let it grow in soil and culture it into a plate, let it grow and them transfer it into soil and let it grow from there

Pollen Tube

* Allows the sperm to move into the ovum
* Many seeds will be produced

Female Reproductive Structure

* In angiosperms
* Stigma
* Style
* Ovary

Stigma

* In angiosperm
* Female structure
* Sticky -- allows pollen/sperm to stick to it
* The top bud

Style

* In angiosperm
* Female structure
* Long part of the pistil
* Leads to the ovary

Male Reproductive Structure

* In angiosperm
* Anther
* Polle
* Filament stalk

Anther

* In angiosperm
* Male reproductive structure
* Pollen comes off of this
* Held up by filament stalk
* The fluffy/bulb-ish part

Filament Stalk

* In angiosperm
* Male structure
* Long sticsk that hold up anther

Sexual Reproduction in **Seedless**

* Includes non-vascular mosses and vascular ferns
* Water must be present for the sperm to swim to female part
* Swimming done by use of flagellum

Sexual Reproduction in **Seed Plants**

* Gymnosperms and angiosperms
* Pollen grains produce sperm cells
* Entire mal gametophyte travels to female
* Pollen grain encases sperm to keep moist

Four Organs of a Flower

* Sepals
* Surround + protect flower bud
* Petals
* Colourful structures that attract pollinators
* Stamens
* Male reproductive organ; contains anther, polle, filament stalk
* Pistil
* Female organ; contains a stigma, style, ovary

Pollination

* Two types
* Animal pollination
* Wind pollination

Animal Pollination

* Insects or small animals move towards flowers looking for nectar
* They carry pollen throughout this process

Wind Pollination

* Lots of light pollen grains are carried in the wind
* Lack colour or odours because it doesn’t need to attract pollinators

Seed Germination

* A seed lands in a reliant area and it begins to resume growth
* Called germination
* Absorbs water, swells, and breaks the seed coat
* The stored food begins to break down and is made available for the embryo

Radicle

* The first thing that emerges from the seed
* Once when it starts germinating and the seed coat comes off, the radicle grows downwards and becomes the root

Hypocotyl

* Small little green loop that emerges from soil
* Becomes the shoot system

Plant Hormones

* Help determine cellular differentiation and gene expression
* Are chemical compounds that send signals between tissues
* 5 main plant hormones:
* Auxins
* Cytokinins
* Gibberellins
* Ethylene
* Abscisic Acid

Stimulatory Plant Hormones

* Auxins
* Cytokinins
* Gibberellins

Auxins

* **Stimulates** elongation of cells


* Regulates expansion of cells in response to gravity or light

Cytokinins

* **Stimulates** production of proteins needed for mitosis (cytokinesis)
* Prevents ageing of leaves by promoting cell division and proteins
* Cell division prevents ageing because it replaces the dead cells with younger cells

Gibberellins

* **Stimulates** seed germination
* Promotes the growth of taller, stronger plants

Inhibitory Plant Hormones

* Ethylene
* Abscisic Acid

Ethylene

* **Inhibitory** hormone
* A gaseous hormone
* **Inhibits** the ripening of fruits and vegetables (slows it down)

Abscisic Acid

* **Inhibits** plant growth by controlling access to CO2 to prevent photosynthesis
* Controls the opening and closing of the stomata

Why are stimuli responses important?

Since plants are anchored down, they need a way to protect themselves.

Nastic Response

* A response to stimuli
* More immediate and temporary
* Plants can move independently from the directin of the stimulus

Tropism

* A response to stimuli
* Affects the way they grow, rather than immediate reactions to stimuli


* Plants can grow towards or away from a stimulus
* 3 responses:
* Phototropism
* Gravitropism
* Thigmotropism

Phototropism

* The cell grows towards the light
* A positive tropism

Gravitropism

* The plant grows in response to gravity