An Introduction to Plants

Main Point #1 Plants are different from algae mainly due to their adaptation to land Plants protect their embryos, allowing them to spread to new environments Plant reproduction is different from protists (such as algae) and animals

What is a plant? Eukaryotic Multicellular Photosynthetic Terrestrial Cellulose in the cell wall NOT A PLANT

Common Features of Plants Photosynthesis in chloroplasts Cellulose in plant cell walls

Secondary Products Unique adaptations of groups of plants Waxy leaves Wood Poisonous leaves Tough seeds/spores Flowers

Embryophytes Major adaptation of plants – the ability of the embryo to survive Can spread to new environments MAJOR difference from algae (not all plants have seeds)

Overview of Plant Reproduction Plants produce both sperm and egg Sperm from one plant travels to another plant – plants don't (usually) fertilize themselves But the way sperm and egg are created is a little different...

Alternation of Generations Plant generations alternate between being diploid (2 copies of chromosomes) and haploid (1 copy of chromosomes) Unlike animals, the haploid generation become multicellular

Mitosis vs. Meiosis Mitosis creates 2 exact replicas of a cell The chromosome number does not change I.e. in humans when we regenerate skin cells Meiosis creates 4 daughter cells Each with half the number of chromosomes I.e. in humans making sperm and egg cells

The Generations Diploid generation is called sporophyte Produces spores via meiosis Spores develop into the haploid generation called the gametophyte via mitosis Gametophytes make gametes via mitosis Gametes fuse to make a sporophyte

Multicellular sperm plant Multicellular egg gametophyte

This is a basic overview... Different divisions of plants differ in their alternation of generations Meiosis makes spores only, all other cells are made via mitosis In primitive plants the haploid generation is dominant, in most others, the diploid stage is dominant

What is the Point of This? As plants adapted to land, it was more difficult to reproduce In water sperm could float to another egg The gametophyte stage likely evolved to produce LOTS of gametes

Main Point #2 All plants originated from green algae The ancestral algae evolved an ability to survive above water The first plants colonized land, opening up an adaptive zone

The Ancestors of Plants Green algae – a photosynthetic protist is thought to be the common ancestor of all plants The specific species of green algae – charophytes

How Do We Know? Homologous chloroplasts (same pigments) Biochemistry- cell walls are similar, % cellulose Mitosis and cytokinesis is similar Sperm ultrastructure DNA analysis

The Evolution of Plants Charophytes lived in shallow water They were likely gradually accumulating traits that helped survive temporary dry periods

Colonizing Land Eventually a population of algae had accumulated enough traits to adapt to land A pond probably dried up and the population survived This would open up a HUGE adaptive zone

Benefits of Land Plenty of space Access to sunlight Abundance of carbon dioxide Rich soil No predators (herbivores) Depiction of the first plants, approx. 400 million years ago

Main Point #3 There were 4 major adaptive radiations of plants (led to 4 major divisions of plants) The first was the colonization of land by what are called bryophytes These plants (mosses) have little structural support, no seeds, no flowers and no vascular system

The First Plants (about 400 mya) Bryophytes  Mosses  Liverworts  Hornworts Lack the ability to move water Sperm needs water to get to egg Gametophyte is the dominant generation

Moss Sporophyte Gametophyte

Liverworts/Hornworts

Moss Lifecycle

Adaptations of Bryophytes The egg and embryo begin developing inside of the parent organism The embryo is protected Spores are hardier and can spread around

Main Point #4 Vascular plants evolved a method of moving water and other nutrients around the plant This allowed them to grow taller and have more separated root and shoot systems

Vascular Plants Evolved the ability to transport water (xylem) and sugar (phloem) around plant Real roots to get water from the soil More developed shoot system to reach higher Can transport materials between the two

Increase in Structure Vascular plants have lignin – a hard material in the cell walls Forms plant “skeleton” Allows taller plants and branching of sporophyte

Seedless Vascular Plants Formed mya i.e. ferns Sporophyte is dominant generation Sperm still requires water to get to egg Still require damp environments Taller and deeper roots

Main Point #5 In seeded plants the gametophytes develop inside the sporophyte Pollen (the male gametophyte) carries sperm to the female gametophyte, forming an embryo Embryos are packed into protective seeds, which help the embryos survive and spread

Gametophytes in Seeded Plants Seeded plants contain their gametophytes in the sporophytes Instead of spreading the spore, these plants spread their seed which contains the new embryo

Seeds Contain:  A diploid embryo  Food supply  Protective coat Seeds can remain dormant for years Under right conditions, seeds will germinate Seeds can be spread

Seeds Develop within Female Gametophyte The megaspore (female spore) forms the female gametophyte or ovule When the egg is fertilized, the ovule forms a seed

Pollen Is the male gametophyte Pollen is protected and can travel When it enters an ovule, the pollen forms a tube to deliver sperm Pollen is not sperm!

Gymnosperms Non-flowering seeded plants Conifers (cone- bearing) are the biggest division Pines, firs, spruces, cedars, cypresses, redwoods etc. Mostly evergreen

Pine Cones There are male and female cones on a conifer tree What we usually focus on as pine cones are female and create the eggs These eggs get fertilized and form a new sporophyte

Gymnosperm Life-cycle

Main Point #6 Angiosperms, or flowering plants, are the most recently evolved type of plant The flower is the reproductive part of the angiosperm Fruits are mature ovaries, which help encourage the spreading of seeds Angiosperms require help from animals to reproduce

Angiosperms – Flowering Plants The flower contains the male and female reproductive organs Pollen is carried from one flower to another usually by insects or birds or by wind Fertilization causes seeds to grow in the ovary

Fruits Mature ovaries form fruits Fruit can be eaten, cling to animals, or help seeds float in wind Helps spread the seeds

Coevolution Some flowering plants have co-evolved with a specific animal Color patterns, scents etc help insects/birds identify plant Ensures that a flower's pollen is carried to the same species Animal gets constant food source

Monocots Have a single seed leaf (cotyledon) Flowers in multiples of 3 Parallel leaf veins Roots are in a bundle, all coming from the stem Usually non-woody

Dicots 2 cotyledons Flower parts in multiples of 4 or 5 Branched leaf veins Roots develop from one main root (radicle) Often woody

Plants Drastically Changed the Environment Lowered amount of CO 2 in air, which cooled down planet Provided oxygen and opportunity for animals to live on land Changed soil and composition of rocks