Seed Germination


Taking care of a plant takes a lot of work, but the end result is usually satisfying. With the right amount of care and proper fertilization the seed can sprout and mature into a healthy plant. 
In order for germination to occur though, sufficient amount of the following are needed: 
1. Water 
2. Oxygen
3. Appropriate temperature


The following steps of germination are shown below: 

Sexual Reproduction in Angiosperms


Since there are two fertilizations occurring, it is called double fertilization.

Plant Hormones


A hormone is a chemical compound produced in one part of the plant that controls growth activity. The hormones in plants stimulate the chemical signals between cells and tissues. Plant hormones can be grouped as a promoter (stimulates growth) or inhibitor (block growth). 

Auxin is an example of a promoter hormone. Auxin stimulates cell division and elongation in stem and roots. It also regulates cell expansion in a plants in response to light and gravity (tropism). The hormone can be found in the apical meristem. Auxins produced by the meristem create an affect called apical dominance, the plant ends up growing taller with fewer side branches. Removing the apical meristem will decrease the amount of auxin, and result in promoted growth of side branches.

Plant Nutrients


There are factors that affect the growth of plants. This includes internal regulators (hormones), external environment (tropism), sunlight, carbon, water, and soil. 
Plants also need a certain amount of nutrients depending on their dry weight. Macronutrients are nutrients needed in created amount than 1% of a plant's dry weight. Micronutrients are needed in smaller amounts (i.e iron, zinc, and copper). Each nutrient has a different affect for plants. Nitrogen gives the plant a dark green colour. Potassium strengthens the plant's disease resistance. Calcium helps develop healthy cell walls. Sufficient amount of nutrients will aid the growth of a healthy plant. 

Tropism



The pictures presented above is the affect of tropism. Tropism is the growth response of a plant to an external stimulus (this can be light, gravity, etc.). Tropism can be negative (growth away from stimulus) or positive (growth towards stimulus). 

Non-Vascular Plants

Classifying Vascular Plants


Most plants today are either angiosperms or gymnosperms. Both types grow from a seed. 


Gymnosperms
Gymnosperms in Greek means "naked seeds". The seeds (ovules) of gymnosperms are not encased in contrast to seeds or ovules of angiosperms. There are less than 900 species of gymnosperms today. The most common gymnosperm are conifers. 




Angiosperms 
The word "angi" in Greek, means enclosed, while sperm means seed.
The embryo of an angiosperm contains a one or two cotyledons which provide nourishment to the embryo. The seeds of an angiosperm is encased and consists of necessary nutrients that help the embryo develop. The embryo of an angiosperm develops inside the seed; this gives angiosperms a stronger advantage than gymnosperms. Angiosperm can be classified depending on what sex cell they carry. 






The following video shows a closer look at the two types of vascular plants and pollination:

Major Angiosperm Classes

	Monocot	Dicot
# Of embryonic seed leaves	One	Two
Organization of vascular tissue in roots and stem	Vascular tissue is arranged in a ring. Vascular bundle is scattered throughout ground tissue.	Vascular tissue is arranged in a star/x-shape. Vascular bundle is arranged in a distinct ring.
Venation	Veins are parallel along the length of the leaf.	Veins are palmate of pinnate.
# Of flower parts	3 parts, of multiples of 3.	4 of 5 parts, or multiples of 4 or 5.
Secondary Growth	No	Yes
Root Systems	Fibrous	Taproot

Dermal Tissue


Dermal Tissue: the outer covering of a plant. In a herbaceous plant, the epidermis (single layer of dermal tissue) forms a protective covering over the plant. Periderm can replace the layer of epidermis in a non herbaceous plant. This secondary growth usually forms cork.


Guard Cells and Stoma 


The stoma is found on the underside of the leaf. It is a pore-like opening and permits gas exchange. The guard cells are lined around the stoma and controls the opening and closing of the stoma. 






Trichomes


Trichomes keep the epidermal surface cool and reduces evaporation. Some trichome release toxic substances to repel insects and some are sharp to puncture predators. 


The Venus fly trap uses its leaves to puncture insects.  



Root Hairs


Root hairs increase the surface area by which the the plant can absorb water and nutrients. 





Ground Tissue: This tissue provides support and store starches. Contains parenchyma, collenchyma, and sclerenchyma cells.


Vascular Tissue


Vascular bundle connects the vascular tissue in the roots with the leaves. The vascular bundle is made of the xylem and phloem. The xylem is made up of non-living tracheid cells. Fluid is passed through pits. In the phloem, materials pass through sieve plates. The phloem is made up of living sieve-tube cells.

Meristematic Tissue


Meristematic Tissue: tissue where cells are constantly dividing and mitosis is restricted to.


There are three types of meristem tissue: 
1. Apical meristem: growth of roots, leaves, and flowers.
2. Intercalary meristem: growth in length of leaves and stem (i.e grass). 
3. Lateral meristem: growth of tissue beneath bark of stems horizontally (i.e growth of tree trunk in girth)


There are two types of lateral meristem:
1. Vascular cambium: production of phloem cells and xylem cells
2. Cork cambium: production of bark 

Plant Cells





Parenchyma Cells:
Flexible thin-walled cells capable of several functions including photosynthesis and storage. These cells are spherical and able to flatten.





Collenchyma Cells: 
Elongated cells that appear in strands provide support for surrounding cells. These cells are flexible and can bend without breaking. 

Sclerenchyma Cells: 
Thick secondary cell walls that provide support for mature plant. These cells contain lignin, a substance that makes cell walls tough and hard. 

Vascular Plant Systems


Shoot system: above ground; stems & leaves. 

Roots


Roots

Three main functions: 
1. Anchors the plant 
2. Take in water and dissolved minerals. 
3. Store carbohydrates 

Two types of root systems : 
Taproot: grows vertically downwards in order to tap into water sources. Forms a center in which roots sprout laterally from. 
Fibrous: does not grow as far as the tap root system. Many thin moderate branching roots.





Root Layers


Epidermis: protects internal roots structures and absorbs water/dissolved minerals from soil.
Cortex: cells have irregular shape and contain large vacuoles for food storage. 
Endodermis: thin layer of cells inside the cortex filters the material travelling towards center of the root.
Vascular tissue: Contains xylem and phloem. It is called the vascular cylinder in roots.  

Leaves & Stem



Stems 
There are many types of stems, ranging from soft and flexible herbaceous, to hard and rigid woody. 




Functions: 
Supportive Role: holds plant up to light.
Nutritional Role: transports water and nutrients through vascular tissue.
















Leaf Layers: 




Epidermis (upper & lower): if unbroken, repels invaders. The cuticle surrounds the leaf, acting as a  waxy covering. This protective layer helps reduce water loss by reducing evaporation. 
Spongy layer (spongy mesophyll): irregularly shapes and loosely packed. Contained in the air spaces of a leaf. These air spaces contain carbon dioxide, oxygen, and nitrogen. 
Vascular Tissue: xylem and phloem forms veins.
Main functions: 
1. Conduct water and dissolved minerals into leaf.
2. Conduct and dissolve carbohydrates out of leaf. 
Palisade Layer (palisade mesophyll): tightly packed cells below epidermis. The structure and shape of the parenchyma cells enable maximum light to penetrate through the transparent layer. This layer contain many chloroplast. Most photosynthesis occurs in this layer. 




  

Transport in Plants: Xylem


Water is then transported through the xylem tissue and diffuses into other tissues of the plant. Entering the leaf, the xylem's conducting vessels branch into numerous veins. At the end of each vein, water and minerals can diffuse not the leaf's cells.  Though much of the water that reaches the leaf, 90% of it, evaporates through the stomata. This process is called transpiration. 
The movement of water in plants seems as a mystery. How can plants transport water at a long distance if they have no muscle? In veins humans have one way valves in veins to prevent the back flow of blood due to gravity, but how is this accomplished in plants?


Long distance transport in the xylem is accomplished by two processes: root pressure (positive pressure), and transpirational pull (negative pressure). Both positive pressure (pushing) and negative pressure (pulling) contribute to the movement of water upwards through the xylem. 


Root Pressure: mechanism by which positive pressure in roots moves water and minerals upward in plants. Water entering the roots creates a positive pressure, pushing water upwards. Minerals from the soil is moved to the xylem against the concentration gradient.

Transpirational Pull: also known as the cohesion-tension model. Recall that most of the water that reaches leaves is evaporated through transpiration. This loss of water creates a negative pressure and pulls the water up to replace the lost water. 
There are three main factors that play a role:
1. Transpiration: evaporation of water through the stomata. Negative pressure exerts tension on the water confined in the xylem's tube down to the roots. 
2. Cohesion: force of attraction between water molecules. This attraction keeps the water column unbroken while being pulled upwards.
3. Adhesion: force of attraction between water molecule and the walls of the xylem. 
Both attractions keep the water column unbroken while being pulled upwards.


The following video explains and illustrates the process of transpiration pull:

Transport in Plants: Phloem


The phloem transports products of photosynthesis (sucrose and other organic molecules) from leaves to roots. Transport of these products through the phloem is called translocation.
Translocation moves sucrose from a source to sink through a combination of osmosis and pressure dynamics. The sink is any region in the plant where sugars are used or stored.





While water and minerals are being pulled up by transpiration, plant nutrients are pushed through the phloem. The movement of water leads to an increase in pressure in the phloem. Pressure gradient between source and sink causes a flow of solution through the phloem and sucrose is removed by the tissues in plant stems and root. Since the concentration of sucrose decreases, water moves out of the phloem and pressure decreases.
In xylem, it is mostly negative pressure that moves the water and dissolved materials, while positive pressure is what drives the flow from source to sink in the phloem.  

Anatomy of a Flower

Plants have been abundant in the Earth for several years. Seed plants first appeared in the fossil record approximately 400 million years ago, while flowering plants appeared in the fossil record approximately 135 million years ago. Over many generations humans developed various uses of plants; food, shelter, medicine, fuel, etc. Plants are significant and vital for our survival.

Issues

Today, we continue to use plants for our various needs. But as we continue to consume, we end up significantly damaging the environment, Through pollution, deforestation, and over consumption, humans are using up more sources on Earth than can be replenished.

Why does this matter?

Ever heard the quote, "If the bee disappears from the surface of the earth, man would have no more than four years to live"? Bees play an important role in pollination. Pollination enables the cycle of fertilization to occur. It is a necessary step for the reproduction of flowering plants. Without pollinators, certain plants won't be able to go through pollination. Fruit, nuts and vegetable crops would be significantly affected by this and food would end up being scarce. Just like humans, animals need plants to sustain life. With food scarce, it will be harder for animals to survive. With less animals and food, it will be harder for humans to survive. And the chain goes on. There is an equilibrium within the ecosystem, it is a cycle that sustains life. Breaking this cycle can cause an ecosystem to be off balance.

Plants are often disregarded in our busy modern world. We begin to interfere with the cycle and destroy the habitats of plants and animals. The damage we've inflicted upon our environment is a current issue and some are trying to accommodate.

What Can I Do?

The little things count. A simple action can go a long way. It is important to be aware about current environmental issues and what you can do to help. Educate yourself and have an understanding of plants and their significance to the environment. This site is for informative purposes, but there are ways to get involve. You can start by clicking the "get involved" section.