Plants
Plants probably evolved from a species of algae that went onshore around 1.2 billion years ago
The first plants were non-vascular plants
Lycophytes were the first plants(still exist)
Some lycophytes evolved into scale trees(extinct)
Scale trees used to covered lots of land, forest of them were very dense{good for coal}, they existed during the carboniferous period
Alternation of generations:
Plants, algae and some invertebrate animals have evolved a cycle where there are 2 different forms involved in reproduction
Each form gives rise to the other form and are considered part of different generations
This evolved initially in algae
In algae, the forms look very similar but in land plants, they look very different
One form is called the gametophyte and the other is called the sporophyte
Gametophyte:
The gametophyte reproduces sexually and makes the haploid gametes
The gametophyte generation are haploid and always either male or female
When the male and female gametes fuse, they give rise to the sporophyte
Sporophytes:
They reproduce asexually and make spores
The sporophyte is diploid and contains a capsule called the sporangium
The sporangium produces spores which are haploid reproductive cells
The sporophyte is attached to the parent gametophyte and derives water and nutrients from it
When the spores disperse and germinate, they produce gametophytes
In non-vascular plants, the dominant phase is the gametophyte,
In vascular plants, the dominant phase is the sporophyte
Pollen is a gametophyte produced by vascular plants, it is not a gamete
Non-vascular plants:
They are also called bryophytes
Plants that don't have specialised conductive tissueTissue for transport of substances
They take moisture from through the cell walls and transport it via osmosis
Minerals are transported via diffusion
Because of the lack of conductive tissue, they have a limited potential for growth
They require water for reproduction
There are currently 3 phylum of bryophytes,
Bryophyta, Hepatophyta and Anthocerophyta
It is unclear which of the 3 phyla evolved the earliest
Bryophyta:
Phylum of bryophytes containing mosses
There are around 15,000 species of mosses
Hepatophyta:
Phylum of bryophytes containing liverworts
There are around 9,000 species of liverworts
Anthocerophyta:
Phylum of bryophytes containing hornworts
There are around 100 species of hornworts
Reproduction of bryophytes:
The male gametophyte makes its gametes in a feature called the antheridia
The female gametophyte makes its gametes in a feature called the archegonia
The male gametes swim from the antheridia to hte archegonia in the presence of water
It then fertilizes the egg and a zygote is formed which undergoes mitosis and eventually forms a sporophyte
The sporophyte grows attached to the mother
After growing, the sporophyte sends out a stalk with a cap on top
The cap provides protection and the made out of the remaining piece of the mother and is called a calyptra
Under the calyptra is the sporangium which makes and contains many spores
The spores are made through meiosis and are haploid
When the sporangium is mature, its lid falls off
When the humidity is high, the spores are let into the wind
When a spore lies on a moist ground, it will germinate and give rise to filaments called protonema
The protonema give rise to buds which grow into a colony of gametophytes
Vascular plants:
Vascular plants are plants that have conductive tissue
Vascular plants which produce unprotected seeds are called gymnosperms
Angiosperms are vascular plants that form flowers, fruits and protect the seeds
Angiosperms developed at the end of the cretaceous period(65 mya)
Primary growth:
Growth that takes place in from the tips of the root or the shootstem and any things that it supports
Primary growth makes a plant grow longer but not wider
Some plants only undergo primary growth and don't grow wider, they are known as herbaceous plants
Herbaceous plants include:
Most plants that complete growing in 1 growth cycleannual plants
Most plants that take 2 years to complete their growthbiennial plants
Some plants that live longer than 2 yearsperennial plants
Secondary growth:
Secondary growth is growth that allows plants to grow wider
This is due to the development of additional tissues, especially woody tissue
This occurs in most plants that produce seedsMonocots usually don't undergo secondary growth
Organs of tracheophytes:
All vascular plants have 3 main organs,
Root:
Absorbs water and nutrients, keeps the plant anchored to the ground
Stem:
Contain structures that transport fluids and nutrients, store nutrients, support the leaves and, contain cells responsible for growth{Meristems}
Leaf:
Where the plant exchanges gases with the atmosphere and undergoes photosynthesis
Tissues present in tracheophytes:
There are 3 types of tissues in vascular plants,
Dermal tissue, ground tissue and vascular tissue
The 3 major organs contain all 3 types of tissue
Dermal tissues:
They make the outermost layer and help prevent damage and water loss
Epidermis:
The dermal tissue contains a layer of cells called the epidermis
The epidermis is the outermost layer of cells in plants
It separates the rest of the plant from the exterior
In leaves and stem it has an outer layer called a cuticle which helps prevent water loss
In some leaves and pods{case that contains seeds of a plant} the epidermis sprouts hair like structures called trichomes
Trichomes provide protection against insects and can secrete toxic or sticky fluids
In leaves, the epidermis has openings called the stomata
The stomata allow intake of air and their shape is regulated by the 2 surrounding guard cells
The guard cells swell when filled with water and move apart, opening the stomata
In the roots, the epidermis has "root hairs" which maximize the surface area of the root helping in absorption
Ground tissue:
The most abundant tissue, they carry out most of the important functions like photosynthesis and storage of food
Mesophyll:
In leaves, water goes from the xylem through vein like structures into the mesophyll
The mesophyll is between the top and bottom epidermis of the leaf
The mesophyll is part of the ground tissue present in the leaf
It is full of parenchyma and collenchyma cells arranged loosely to let material flow between them
Chloroplasts are present in the mesophyll and photosynthesis occurs here
Vascular tissues:
Conduct water, food and minerals from the environment to the plant
Xylem:
It carries water and dissolved minerals from the root to other parts of the plants
It contains 4 main types of cells,
Xylem parenchyma:
The only alive part of the xylem
They assist in short distance water transport and, store starch and fat
Xylem fibers:
They have lignified walls and a central lumen{Empty hole}
They provide mechanical support and transportation of water
Xylem vessel:
Long tube-like cells with lignified walls
At maturity the living part of the cell dies and disappears
Vessel members are interconnected with each other through small holes present in their walls
They are present in most angiosperms and some gymnosperms
They transport water and minerals and, provide structure to the plant
Tracheid:
Tube-like cells containing a thick lignified wall
They lack the living interior and only have the wall
They are present in most gymnosperms and angiosperms
They transport water and provide structural support
Tracheids, xylem fibers and xylem vessels are types of sclerenchyma cells
Phloem:
A type of vascular tissue that transports food made from photosynthesis{AKA the sugar}
The phloem uses active transport while the xylem mostly uses passive transport
The sugar is transported in the form of sap, water rich in sugar
There are 4 types of phloem cells:
Phloem parenchyma:
Undifferentiated parenchyma cells present in the phloem
They are used for food storage
Companion cell:
Specialised parenchyma cells
They have a dense cytoplasm and carry out cellular function of the sieve tubes
The wall shared by the sieve tube and companion cells have a large number of channels in them{plasmodesmata}
They are classed in to 3 types,
ordinary companion cells, which have few or no channels with non-sieve tube cells,
Intermediary cells, which have many vacuoles and channels and synthesize RFOs{second most abundant family soluble carbohydrate} and,
Transfer cells which have large surface are due to folded walls
Sieve tube:
They are the major conducting cells in the phloem
They have pores allowing for connection to neighboring cells
They have very few or even no ribosomes and, they lack a nucleus
They run parallel to the tissue that they are in
Phloem fibers:
Plant fiber present in the phloem
They are long, narrow supportive cells and provide strength while allowing flexibility
They are the only non living part of the phloem
Cells present in tracheophytes:
Parenchyma:
The most abundant cells, they are found in roots, stem, leaves, flowers and other parts of plants
They are thin and perform many actions
It makes up the cortex
Collenchyma:
Elongated cells with thick cell walls
They help hold up the plant body, especially in herbaceous and young plants
Sclerenchyma:
Cells with very thick cell walls made from lignin
Most sclerenchyma cells die when they reach maturity, leaving behind their cell walls for support
New cells push the old cells outward creating rings
In warm, wet years the layers are thick and in cold, dry years the layers are thin
Path of water through the plant:
The water travels through the root hairs present in the epidermis to a strachy layer called the cortex
From the cortex the water travels to the xylem
From the xylem, the water travels to the shoot due to evapotranspiration in the leaves
From the leaves in the shoot, the water is mixed with sugar to form sap and goes to other parts of the plant through the phloem
Evapotranspiration:
In the arial parts of the plant, water evaporates creating less pressure at the top
This helps cool down the plant and helps carry water through the xylem to the leaves
Only around 1% of the water absorbed by plants is used by them, the rest is evaporated
This occurs when the stomata is open
Vascular plant reproduction:
They utilize alternation of generations similar to bryophytes
Instead of being gametophyte dominant like bryophytes, they are sporophyte dominant
Ferns:
They reproduce in a similar manner to bryophytes,
They have spores that grown on the underside of the leaf, which are released and need moist ground to germinate
This make a gametophyte that is a few centimeters wide
The gametophyte contains both male and female reproductive organs
When the gametes meet, they will create the sporophyte which is recognizable as a fern
Pollen:
Most tracheophytes other than ferns produce pollen
Pollen is a male gametophyte that produces male gametes
Pollen grains have a hard coat to protect the gametophyte in travel
The pollen contains vegetative cells and generative cells
Ovules:
It is the structure that contains the female gametophyte in seed producing plants
When the gametes meet, they produce a seed which can produce a plant, specifically the sporophyte
Gymnosperms:
They include conifer, gingkos, cycads and others
They don't produce flowers, they use cones as reproductive structures
Their ovules develop exposed to the elements at the base of the cone scales
The male cones are smaller and spongy and the female cones are recognizable as cones
When the pollen made by the male cone reaches the ovule at the base on the cone scales, it fertilizes it
The embryo matures inside the female cone and makes a seed
This seed has enough nutrients to sustain it after germination until it is older
The seed has a shiny casing that protects it from the outside
When the seed is mature, the scales of the cone and the seed falls and is carried by the wind
Some gymnosperms have special conditions that must be meet for it to disperse the seeds
Angiosperms:
They have seeds and flowers
Flowers tend to use animals for pollination
The flowers and pollinators{animals involved in pollination} probably co-evolved
Pollinators get food{nectar} and the flowers disperse their gametophytes
All parts of the plant other than the ovum and the pollen are sporophytes
Perfect flowers are flowers containing both male and female gametophytes
The gametophytes in non perfect flowers maybe in the same plant and different flowers or different plants
Structure of a perfect flower:
They contain sepals, petals, stamen, pistil
The sepal covered the flower when it was a buds
The petals are colored to attract pollinators
The stamen is the male reproductive part
It contains the anther which makes pollen and a filament which is a long tube at the base of the anther
The pistil is a vase like structure that contains the female reproductive system
The ovules are present in the ovary present at the bottom of the pistil
The pistil contains a long neck called a style and opening at the top called stigma
The style and stigma are involved in preventing self fertilization
The style prevents the growth of pollen tubes in cases of self fertilization
Pollination:
The transport of the male gametophyte to the female gametophyte
The flowers attract pollinators using smells, color, food to spread the pollen
Fertilization:
The stigma receives the pollen
The vegetative cells of the pollen produce a tube connecting to the ovary and opening in the ovule
The generative cell divides and 2 sperm are formed
The 2 sperm travel down the tube to ovules
The ovule is arranged in a 3 + 1 + 3, with 3 antipodal cells at the top, 1 central cell, 2 synergids and an egg cell at the bottom
The antipodal cells provide nourishment for the egg
The central cell is diploid and becomes the endosperm
The synergids guide the pollen tube
The egg becomes the embryo
The 2 sperm fertilize the central cell and the egg cell
The central cell becomes the endosperm which provides nutrition and is triploid
The egg cell becomes the embryo
The fertilization of the ovule is called double fertilization as the central cell and the egg are being fertilised
After fertilization,
The ovule swells and the wall tightens and becomes a seed
The ovary grows around it and becomes a fruit
The fruit contains the seeds and disperses via animals or the elements
This is to avoid competition for resources with its parents