Unit 6

Microorganisms

Prokaryotes, Viruses, Protists, Fungi and Plants

20.1: Viruses

Discovery of Viruses

• 1892: Dmitri Ivanovski discovers that something in a liquid from infected plants caused the disease
• 1897: Martinus Beijerinck suggests that tiny particles in the juice caused the disease and called them viruses
• 1935: Wendell Stanley isolated crystals from the juice. SInce living things don’t crystalize, Stanley concluded that viruses weren’t really alive.

20.1: Viruses

Viruses are extremely small and can only be seen with an electron microscope.

The protein coat around the virus is called a capsid.

The simplest viruses have only a few genes. more complex viruses can have hundreds of genes.

20.1: Viruses

Most viruses have proteins on their outer surface that interact with the receptor proteins on the cell membrane. These proteins “trick” the cell to take the virus, or its genetic material into the cell.

Once inside the cell, the virus takes control of the cell and uses the cell to make more viruses.

20.1: Viruses

Since viruses must bind to specific proteins on the cell’s surface, most viruses only infect certain species of plants, animals, and bacterial cells.

20.1: Viruses

• Inside living cells, viruses use their genetic information to make copies of themselves.
• Some viruses replicate immediately and others remain inactive within the host.
• There are two types of bacterial viral infections (bacteriophages)
• Lytic infection: A virus enters the cell, makes copies of itself, and causes the cell to burst, or lyse.
• Lysogenic infection: The virus DNA is inserted into the cell’s DNA. Each cell division results in daughter cells with viral DNA in their genome.
• Viral infections in eukaryotic cells is similar to the lytic and lysogenic infections of bacteria.

20.1: Viruses

• Lytic and lysogenic infections in bacterial cells.
• The dormant viral DNA is called a prophage.

20.1: Viruses

• About 70% of viruses contain RNA instead of DNA
• Cold viruses:
• The virus capsid lands on the cell surface and is brought into the cell.
• The viral protein makes copies of the RNA
• The cell’s ribosomes are tricked into treating the virus RNA as cell mRNA and they produce capsids and other viral proteins.
• The new capsids assemble around the viral RNA copies and the cell releases hundreds of new viral particles that will infect other cells

20.1: RNA Viruses - The Common Cold

20.1: Viruses

• About 70% of viruses contain RNA instead of DNA
• HIV is a member of RNA viruses called retroviruses. Genetic information of the retrovirus is copied from RNA to DNA instead of DNA to RNA.
• A retrovirus invades a cell and it makes a DNA copy of its RNA. It is the DNA copy that is inserted into the host DNA.
• Retroviruses are similar to lysogenic viruses
• The cell produces the viral particles that eventually kill the cell

20.1: RNA Viruses - HIV

20.1: Viruses

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20.2: Prokaryotes

Classifying Prokaryotes

• Prokaryotes are the smallest and most abundant microorganism on Earth
• Prokaryotes are unicellular organisms that lack a nucleus.
• Prokaryotes have DNA but their genetic material is not bound up in a membrane-bound nucleus.

20.2: Prokaryotes

Classifying prokaryotes

• Prokaryotes are the smallest and most abundant of microscopic life
• Prokaryotes are classified as Bacteria or Archaea (two of the three domains of life)
• Eukarya is the third domain
• The domain Bacteria corresponds to the kingdom Eubacteria
• Archaea corresponds to the kingdom Archaebacteria

20.2: Prokaryotes

20.2: Prokaryotes

Bacteria

• Usually surrounded by cell wall
• Pili are used to anchor the bacterium to surfaces
• Flagella are used for movement

20.2: Prokaryotes

Archaea

• Look similar to bacteria
• Differences
• Lack the layer that surrounds the cell membrane
• Archaea membranes contain different lipids
• DNA sequences are more similar to Eukaryotes
• Many live in harsh (high temperature, highly salty, low or no oxygen) environments

20.2: Prokaryotes

Structure and Function

• Prokaryotes vary in their size, shape, how they move, and the methods in which they obtain and release energy.

20.2: Prokaryotes

Size, Shape, and Movement

• Much smaller than most eukaryotic cells
• Three shapes (rod, sphere, and spiral)
• Some depend on outside forces to move them or by swarming where the binary fission of the colony moves the colony through its outward growth. Others are propelled by flagella and others glide along the film of slime they secrete.

20.2: Prokaryotes

Nutrition and Metabolism

• Heterotroph “other feeder” - Takes in organic molecules from the environment or other organisms
• Photoheterotroph “light and other feeder” - Like heterotrophs but also captures light energy
• Photoautotroph “light self-feeder” - Uses light energy to convert CO₂ into carbon compounds
• Chemoautotroph “chemical self-feeder” - Uses energy released by chemical reactions involving ammonia, hydrogen sulfide, and other chemicals

20.2: Prokaryotes

Growth, Reproduction, and Recombination

• Prokaryotes will divide after their cell size has doubled when the organism splits into two daughter cells.
• This is asexual reproduction through binary fission
• Under favorable conditions, prokaryotes can divide every 20 minutes
• When conditions are harsh, prokaryotes can form endospores. These thick walled structures surround the cell protecting the DNA and some cytoplasm. When conditions improve the endospore opens and the bacteria resume their normal activities

20.2: Prokaryotes

Growth, Reproduction, and Recombination

• Mutations are the main way that prokaryotes evolve.
• Changes to DNA are passed on to the daughter cells during binary fission
• Conjugation - Many prokaryotes exchange genetic material through a process called conjugation where plasmids are exchanged between bacteria. The plasmids contain genes that
• enable a bacteria to survive environmental conditions
• resist antibiotics
• increase the genetic variability in prokaryote populations

20.2: Prokaryotes

The Importance of Prokaryotes

• Prokaryotes are essential in the ecological balance of the planet
• Decomposers - Breaking down organic molecules into simpler forms provides living with raw materials for other organisms
• Producers - Photosynthetic prokaryotes are responsible for more than half the primary production on the open ocean. Food chains are dependent on these organisms
• Nitrogen fixers - Nitrogen is necessary for proteins and other molecules. Prokaryotes are one of only a few organisms that can take atmospheric nitrogen and fix it into forms that other organisms can use.

20.3: Diseases Caused by Bacteria and Viruses

Bacterial Diseases

• Microorganisms (prokaryotes and viruses) that cause disease are called pathogens.
• Bacteria cause disease by
• destroying living cells
• releasing toxins (poisons) that upset homeostasis
• botox is a poison produced from the botulinum toxin
• tetanus

20.3: Diseases Caused by Bacteria and Viruses

Bacterial Diseases

• Controlling bacteria
• Physical removal - washing hands or other surfaces
• Disinfectants - chemical solutions kill bacteria
• Food storage - low temperatures slow the growth of bacteria
• Food processing - cooking food raises temperatures that kill bacteria and denature most toxins. Ultraviolet light will also sterilize prepared foods
• Heat sterilization - medical instruments are placed in autoclaves that produce high temperatures that kill bacteria.

20.3: Diseases Caused by Bacteria and Viruses

Bacterial Diseases

• Preventing and Treating Bacterial Diseases
• Vaccines - A preparation of weakened or killed pathogens or inactivated toxins (think snake serum) that cause the body to produce immunity.
• Antibiotics - These are drugs that block the growth and reproduction of bacteria

20.3: Diseases Caused by Bacteria and Viruses

Viral Diseases

• Preventing and Treating Viral Diseases
• Viruses attack and destroy certain cells in the body
• Some viruses affect the pattern of growth of cells, sometimes leading to cancer
• Vaccines - Most often the best way to prevent viral diseases. Behaviors that reduce the transmission of viruses between people are also effective.
• Antibiotics - Are useless against viruses. There are a few effective antiviral drugs that attack viral enzymes.

20.3: Diseases Caused by Bacteria and Viruses

Emerging Diseases

• Emerging diseases are a greater danger to human health
• Human populations have little or no resistance to them
• Methods of control have not yet been developed
• “Superbugs” that are resistant of all known antibiotics
• New viruses
• Genetic changes occur often in viruses to the point where viruses can jump from one host species to another
• Bird Flu, ebola, and HIV

Short answer questions on Chapter 20 test

One of these two questions will appear on the test

• How do bacteria cause disease?

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• Why are emerging diseases particularly threatening to human health?

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21.1: Protist Classification

The First Eukaryotes

• Protists are eukaryotes (organisms whose cells contain a membrane-bound nucleus and organelles) that are not members of the plant, animal, or fungi kingdoms
• Most protists are unicellular
• Protists are more diverse than any other kingdom
• The classification of protists (and plants and animals) will probably change as new research into the relationships between these groups continue

21.1: Protist Classification

The First Eukaryotes

21.2: Protist Structure and Function

How Protists Move

• Changing cell shape
• Pseudopods - Projections of the cytoplasm called amoeboid movement.
• Powered by a cytoskeletal protein called actin
• https://www.youtube.com/watch?v=o-PjvIRrbbw

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21.2: Protist Structure and Function

How Protists Move

• Cilia and Flagella
• Cilia - Short hair-like structures that move somewhat like oars on a boat
• Many cilia are found on the outside of protists
• Flagella - Long hair-like projections that can rotate or move in a wavelike motion.
• Cells usually have one or two flagella
• Passive movement
• Require wind, water, or other organisms to move from place to place
• These protists form reproductive spores

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21.2: Protist Structure and Function

How Protists Move

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21.2: Protist Structure and Function

Protist Reproduction

• Cell division
• Asexual reproduction - Reproduction through the process of mitosis. Daughter cells are identical to the parent cell
• Conjugation - Under stressful conditions:
• Two organisms exchange genetic material followed by reproduction by mitosis.
• Conjugation results in more genetic variability

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Conjunction

21.2: Protist Structure and Function

Protist Reproduction

• Sexual Reproduction
• Many protists have complex sexual life cycles alternating between haploid and diploid phases
• The process is called alternation of generations

Alternation of Generations

21.3: The Ecology of Protists

Autotrophic Protists

• Photosynthetic protists play major ecological roles
• Form the base of the ocean food chain
• Symbiotic protists in corals help to produce reef habitats
• Kelp, the largest protist, provides shelter for many ocean species
• Rapid growth of protists due to high levels of nutrients depletes nutrient levels, lowers oxygen levels as dead protists decay, and some protists produce toxins that poison fish and shellfish.

21.3: The Ecology of Protists

Heterotrophic Protists

• Some heterotrophic protists engulf and digest their food.
• Amoeba feeding https://www.youtube.com/watch?v=pvOz4V699gk
• Paramecium feeding https://www.youtube.com/watch?v=sn3MTYNe8mM

21.3: The Ecology of Protists

Heterotrophic Protists

• Some heterotrophic protists absorb their food from the environment
• Play a very important role in the recycling of nutrients

21.3: The Ecology of Protists

Symbiotic Protists

• Some protists live their lives in a close relationship with another species
• Mutualists - The protist and the host both benefit from the relationship
• Trichonympha and termites. The protist lives in the gut of termites and is able to break down the cellulose of wood fibers and both use the nutrients from the digested wood.

21.3: The Ecology of Protists

Symbiotic Protists

• Some protists live their lives in a close relationship with another species
• Parasites - Parasitic protists are responsible for some of the world’s deadliest diseases.
• Entamoeba (amebic dysentery)
• Cryptosporidium (resistant to chlorine treatment of drinking water)
• Giardia (causes severe digestive problems)
• Plasmodium (malaria) requires two hosts to complete its life cycle

21.3: Plasmodium Life Cycle

21.4: Fungi

Structure and Function

• Fungi are heterotrophic eukaryotes with cell walls that contain chitin
• Two general growth patterns among fungi
• Yeasts are tiny fungi that live most of their lives as single cells
• Mushrooms and other fungi have bodies made of many cells that form long slender filaments called hyphae
• Cross walls between cells contain openings through which cytoplasm and organelles can move.
• The portion of a mushroom above ground is the spore producing structure which grows from the below-ground mycelium.

21.4: Fungi

Reproduction

• Fungi can reproduce asexually by releasing spores.
• Other forms of asexual reproduction arise when hyphae are broken off or the fungus will reproduce by budding (yeast)
• Fungi can also reproduce sexually
• Bread mold does not have male/female but rather two different strains.
• When hyphae of opposites meet, they fuse together to begin the process of sexual reproduction
• The combined cells form diploid zygotes which go through meiosis to form haploid spores. Each spore has different combinations of genetic material

21.4: Fungi

Ecology

• Decomposers
• Many fungi get their nutrients from dead organisms
• Fungi secrete digestive enzymes that break down the tissues of dead organisms.
• Fungi return the nutrients in those organisms to the soil
• Without decomposers such as bacteria and fungi, new life would be impossible.

21.4: Fungi

Ecology

• Parasites
• Plant diseases caused by fungi
• Smuts and rusts are responsible for about 15% of crop losses. Even more in tropical areas.
• Animal diseases
• Fungal infections affect different animal species
• Athlete’s feet
• Thrush - the yeast Candida albicans is usually controlled by the presence of bacteria. Antibiotics kill off most of the bacteria allowing the yeast to proliferate.

21.4: Fungi

Ecology

• Mutualism
• Lichen - Some fungi form mutualistic relationships with photosynthetic organisms (cyanobacteria and/or algae)
• Lichen grow in harsh environments and are some of the first to enter barren areas
• Fungus provides water and minerals and protection from too intense sunlight
• The photosynthetic partners provide food to the fungus.

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21.4: Fungi

Ecology

• Mutualism
• Mycorrhizae - symbiotic relationship with the roots of plants
• Estimated 80% to 90% of all plant species form mycorrhizae with fungi
• Many trees cannot survive without fungal symbionts

22: Introduction to Plants

22.1: What is a Plant?

22.2: Seedless Plants

22.3: Seed Plants

22.4: Flowering Plants

22.1: What is a Plant?

Characteristics of Plants

• Plant kingdom (Plantae)
• Plants are eukaryotes with
• cell walls that contain cellulose
• Carry out photosynthesis using chlorophyll a and b
• Most are autotrophs
• Some are saprobes (feed on decaying organic matter)

22.1: What is a Plant?

Plants have developed adaptations to survive as stationary organisms

• Sunlight - plants use energy from the sun to carry out photosynthesis
• Photosynthetic organs are arranged to absorb the most light
• Leaves are broad and flat

22.1: What is a Plant?

Plants have developed adaptations to survive as stationary organisms

• Gas exchange
• Plants do need oxygen for respiration
• Excess oxygen must be released and carbon dioxide brought in without losing water through evaporation.

22.1: What is a Plant?

Plants have developed adaptations to survive as stationary organisms

• Water and minerals
• Water is needed to replace water lost through evaporation and for photosynthesis
• Minerals from the soil are needed for plant metabolism and growth

Plant Needs

• Sunlight
• Gas exchange
• Water and Minerals

What adaptations do plants have to meet their needs?

22.1: What is a Plant? History and Evolution

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The ancestors of land plants were water dwelling organisms similar to green algae

The first land plants (475 million years ago)

• lacked leaves and roots
• greatest challenge was to obtain water (grew next to wet areas)
• early plants depended on water to complete life cycles

22.1: What is a Plant? History and Evolution

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Plants began to change the environment

• new ecosystems were formed
• organic matter became an important part of soil
• these changes allowed new species of plants to emerge

22.1: What is a Plant? History and Evolution

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22.1: What is a Plant? The Plant Life Cycle

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Land plants have a sexual life cycle different than most organisms

• Alternation of Generations
• Multicellular diploid (2N) stage is the sporophyte or spore producing plant
• Multicellular haploid (N) stage is the gametophyte or gamete producing plant

22.1: What is a Plant? The Plant Life Cycle

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• Sporophyte produces haploid spores through meiosis
• The spores grow into gametophytes
• Gametophytes produce sperm and egg cells which unite
• To produce a diploid zygote which develops into a new sporophyte

22.1: What is a Plant? The Plant Life Cycle

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• A trend in plant evolution is the reduction in size of the gametophyte and increased size of the sporophyte

22.2: Seedless Plants: Green Algae

• The fossil record suggests that green algae were the first plants
• Green algae share characteristics with more complex plants
• Photosynthetic pigments
• Cell wall composition
• Green algae are mostly aquatic
• They make direct contact with the water in which they grow and absorb the nutrients from their surroundings
• Green algae do not have specialized tissues that are found in other plants

22.2: Seedless Plants: Green Algae

• The life cycles of green algae alternate between haploid and diploid phases.
• There may not be a switch every generation.
• Haploid phases can last many generations when conditions are suitable.
• Unfavorable conditions trigger sexual reproduction
• Gametes fuse to form a diploid zygote (sporophyte)
• When conditions improve, the zygote undergoes meiosis and the haploid generations follow

22.2: Seedless Plants: Life cycle of a green algae

22.2: Seedless Plants: Green Algae

• Many green algae form colonies, suggesting how the first multicellular plants evolved.
• The cells are connected by cytoplasm, enabling cells to communicate.
• A few gamete producing cells are specialized for reproduction

https://www.youtube.com/watch?v=He9FSeGRi3A&list=PLb3HuLasLM5Arb5wWL6HAIEkKOSRxgHUM

https://www.youtube.com/watch?v=Cor_ek7foVM

22.2: Seedless Plants: Mosses and other bryophytes

• Bryophytes have specialized sexual reproductive organs
• Bryophytes show a higher degree of cell specialization
• Bryophytes include mosses, hornworts, and liverworts
• Bryophytes are small
• Bryophytes do not have vascular tissue
• Water can’t travel upward through the moss more than a meter
• Moss bodies cannot support a tall plant without cell walls strengthened with lignin

https://www.youtube.com/watch?v=iWaX97p6y9U&list=PLKGQ09wcSS8_3ggPgyRUuC7L8xh3or259

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22.2: Seedless Plants: Mosses and other bryophytes

• Bryophytes display an alternation of generations
• The gametophyte is dominant and carries out most of the photosynthesis
• Sperm cells must have water to swim to the bryophyte egg (another reason why bryophytes are only found where there is water)

22.2: Seedless Plants: Mosses and other bryophytes

• The sporophyte is dependent on the gametophyte for water and nutrients.

Nonvascular plants https://www.youtube.com/watch?v=iWaX97p6y9U&list=PLKGQ09wcSS8_3ggPgyRUuC7L8xh3or259

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22.2: Seedless Plants: Vascular Plants

• The advent of vascular tissue allowed plants to grow taller.
• Vascular tissue transports water and nutrients more efficiently than from diffusing from cell to cell as in the bryophytes
• Vascular plants are also known as tracheophytes - named after the specialized cells, tracheids (tubelike cells strengthened by lignin).
• Tracheids are found in xylem a tissue that transports water upward from the roots.
• Openings between the tracheids (pits) allow water to pass throughout the plant

22.2: Seedless Plants: Vascular Plants

• A second transport tissue is phloem.
• Phloem transports the products of photosynthesis throughout the plant
• Structure of phloem cell are similar to the structure of xylem cells

22.2: Seedless Plants: Vascular Plants

• Vascular tissue is found in many groups of plants that do not produce seeds
• Club mosses, horsetails, and ferns
• Ferns have true vascular tissue, strong roots, underground stems called rhizomes, and large leaves (fronds).
• Ferns are most abundant in wet or seasonally wet areas
• The life cycle of ferns has the diploid sporophyte stage dominant
• The gametophyte stage is tiny compared to the sporophyte
• Reproduction is very similar to the bryophytes

Vascular plants: https://www.youtube.com/watch?v=h9oDTMXM7M8&index=37&list=PL3EED4C1D684D3ADF

22.2: Seedless Plants: Vascular Plants

• Reproduction is very similar to the bryophytes
• Sperm require water to swim from the antheridia to the egg in the archegonia

22.3: Seed Plants: The importance of seeds

• A seed is a plant embryo and a food supply encased in a protective cover.
• The embryo is diploid and is the early stage of development in the sporophyte phase,
• Seed plants do not need standing water for fertilization
• Reproduction takes place in cones or flowers
• Sperm is transferred by pollination
• Male gametophytes and female gametophytes grow and mature within the sporophyte

22.3: Seed Plants: The importance of seeds

• Gymnosperms “naked seed” bear their seeds directly on the scales of cones
• Angiosperms “enclosed seed” bear their seeds in flowers inside a layer of tissue that protects the seed

22.3: Seed Plants: The importance of seeds

• Gymnosperms “naked seed” bear their seeds directly on the scales of cones
• Reproduction takes place in cones.
• Two types of cones (pollen cones and seed cones)
• Male cones produce pollen (the gametophyte stage)
• One of the haploid nuclei in the pollen grain divides to produce two sperm nuclei

22.3: Seed Plants: The importance of seeds

• Female cones produce female gametophytes. At the base of each scale of the cone are two ovules
• Within the ovules meiosis produces haploid cells that grow an divide to produce female gametophytes.
• Each gametophyte contains a few large egg cells

22.3: Seed Plants: The importance of seeds

• The typical conifer life cycle takes 2 years to complete
• A pollen grain is caught in the sticky secretion of the female cone and pulled inside toward the ovule
• The pollen grain splits open and grows a pollen tube which contains two haploid sperm nuclei
• When the pollen tube reaches the female gametophyte, one sperm nucleus disintegrates
• The other nucleus fertilizes the egg and produces a diploid zygote, which grows into an embryo which is encased within a seed

22.3: Seed Plants: Pine Life Cycle

22.4: Flowering Plants

Advantages of flowers

• Flowers attract bees, moths, butterflies and hummingbirds
• These animals are attracted to the flower’s color, scent, shape, and to the flower’s nectar
• The animal will carry pollen from one flower to another
• Pollination this way is more efficient than by wind

22.4: Flowering Plants: Advantages of flowers

https://www.youtube.com/watch?v=ExaQ8shhkw8&list=PL3EED4C1D684D3ADF&index=38

22.4: Flowering Plants

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Advantages of fruit

• After pollination the ovary develops into a fruit
• The fruit is a structure that contains one or more mature ovaries
• The fruit helps disperse the seeds inside it
• Animals eating the fruit carry the seeds far away from the parent plant

22.4: Flowering Plants

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Angiosperm Diversity

• Angiosperms are classified according to
• the number of seed leaves
• the strength and composition of their stems
• The number of growing seasons they live

22.4: The number of seed leaves

22.4: Herbaceous and woody plants

Woody plants

• Cells of the stem have thick cell walls that support the body
• Include trees, shrubs, and vines

Herbaceous plants

• Plant stems are smooth

22.4: Herbaceous and woody plants

22.4: Annuals, Biennials, and Perennials

23: Plant Structure and Function

23.1: Specialized Tissue in Plants

23.2: Roots

23.3: Stems

23.4: Leaves

23.5: Transport in Plants

23.1: Plant Structure and Function: Specialized Tissue

• The three principal organs of seed plants are roots, stems, and leaves.
• Roots anchor the plant in the soil, absorb and transport water and minerals to the rest of the plant, hold the plants upright
• Stems provide the support structure, transports materials and water, supports leaves
• Leaves are the main photosynthetic organs, control water loss, and are the sites of gas exchange

Principal organs of plants

• Leaf - What is its function? What does it need from the plant?
• Stem - What is its function? What does it need from the plant?
• Root - What is its function? What does it need from the plant?

23.1: Plant Structure and Function: Specialized Tissue

• Dermal tissue
• Single layer of cells
• Often covered with a waxy layer (cuticle) protection against water loss
• Some epidermal cells have tiny projections (trichomes) which protect the leaf and give the leaf a fuzzy appearance
• Dermal tissue may be several layers thick and covered with bark
• Includes root hair cells that help absorb water

23.1: Plant Structure and Function: Specialized Tissue

• Vascular tissue
• Long cylindrical cells that connect like pipes
• Two kinds: xylem and phloem
• Xylem carries water
• Phloem carries dissolved food

23.1: Plant Structure and Function: Specialized Tissue

• Xylem
• Xylem cells die after maturing
• Tracheids (all plants) are long cells with cell walls containing lignin
• Vessel elements (angiosperms) are wider than tracheids. Dead tracheids allow the free movement of water.
• Water and minerals move in only one direction; roots to the rest of the plant

23.1: Plant Structure and Function: Specialized Tissue

• Phloem
• Phloem cells are alive at maturity
• Nutrients move in two directions
• Sieve tube elements form sieve tubes
• Ends of the tubes have many holes through which nutrients move. Mature cells are kept alive by
• Companion cells which support the phloem cells and aid in the movement of materials through the phloem

23.1: Plant Structure and Function:

• Plant growth and meristems
• Meristems are regions of unspecialized cells in which mitosis produces new cells that are ready for differentiation (like stem cells)
• Found where plants grow rapidly (tips of stems and roots)
• Apical meristems (found at the apex - tips of stems and roots)
• Eventually the descendents of apical meristem cells become dermal, vascular, or ground tissue
• Floral meristems produce the tissues of flowers including the reproductive organs and the petals.

23.1: Plant Structure and Function:

23.2: Roots

• Tap root - Primary root
• Grows long and thick with smaller branch roots
• Tree taproots can grow several meters below ground
• Tap roots of carrots, beets, other root crops store sugars and starches

23.2: Roots

• Fibrous roots
• Root system of other plants begins with one primary root but is replaced by roots of the same size growing out from the base of the plant stem
• Grasses have fibrous root systems that spread out over wide distances
• Fibrous systems help to prevent soil erosion

23.2: Roots - Anatomy of a root

• Roots contain cells from three tissues - dermal, vascular, and ground tissue
• Epidermis: protection and absorption. Includes root hairs
• Ground tissue: cortex; water and minerals pass through the cortex. Also stores sugars and starch
• Vascular tissue: carries water and minerals to the main part of the plant

23.2: Roots - Root functions

• Uptake of plant nutrients from the soil
• Plants need inorganic nutrients to grow, flower, and produce seeds
• Most important nutrients are nitrogen, phosphorus, potassium, magnesium, sulfur, and calcium
• Other trace elements are also important (iron, zinc, molybdenum, boron, copper, manganese, and chlorine)

23.2: Roots - Essential plant nutrients

23.2: Roots - How do materials get into plants?

Vascular plants: https://www.youtube.com/watch?v=h9oDTMXM7M8&index=37&list=PL3EED4C1D684D3ADF

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23.3: Stems

• Three main functions of stems
• Stems produce leaves, branches and flowers
• Stems hold up leaves to the sun
• Stems transport substances throughout the plant
• Stems contain the three tissue systems: dermal, vascular, and ground tissues
• Buds contain apical meristems
• Larger plants have stems that produce woody tissue

23.3: Stems

• Vascular Bundle Patterns
• Monocots: vascular bundles are scattered throughout the stem.
• Dicots: vascular bundles are arranged in a cylinder or ring.

23.3: Growth of Stems

• Primary growth - Growth by the apical meristem adds length to the plant
• Secondary growth - Stems and roots grow thicker. Common among dicots and nonflowering seed plants. Rare in monocots. Takes place in meristems called vascular cambium and cork cambium

23.3: Growth of Stems

• Vascular cambium produces vascular tissue.
• Cork cambium produces the outer covering of stems

23.3: Growth of Stems

• Divisions in vascular cambium produce new layers of xylem and phloem and the stem becomes thicker.

23.3: Growth of Stems - Formation of Wood

• Wood is layers of secondary xylem produced by vascular cambium built up over years and years of growth
• The older xylem near the center of the stem no longer conducts water. Its purpose is to support the stem (heartwood).
• The xylem closer to the outside of the stem still actively transports water (sapwood)
• In temperate regions, tree growth is seasonal. Spring growth is rapid resulting in light colored rings. Later growth results in darker bands. The rings can indicate the age of woody plants.

23.3: Growth of Stems - Formation of Wood

23.4: Leaves

• Anatomy of a leaf
• Leaf blade - flat shape maximizes the amount of light that is absorbed.
• The leaf is attached to the stem by a thin stalk called a petiole.
• Leaves are covered in dermal tissue and the inner leaf is composed of ground and vascular tissue.

23.4: Leaves

• Dermal Tissue
• The epidermal cells are tough and resist tearing.
• Epidermis is nearly always covered by a waxy cuticle to prevent water loss through evaporation.

23.4: Leaves

• Vascular tissue
• The vascular tissues of the leaves are directly connected to the vascular tissues of the stem. Xylem and phloem tissues are bundled in leaf veins.

23.4: Leaves

• Ground tissue
• Leaves contain special tissue called mesophyll where photosynthesis occurs.
• Sugars produced in mesophyll tissue enter phloem tubes for transport to the rest of the plant.

23.4: Leaves

• Photosynthesis
• Palisade mesophyll: cells just below the upper epidermis
• Spongy mesophyll below the palisade layer allows gases to flow. The spaces are connected to the outside through stomata.

Palisades

23.4: Leaves

• Transpiration
• The mesophyll cell walls need to be moist so gases can diffuse through the cell walls
• Water loss occurs as the water evaporates
• Transpiration is the loss of water through the leaves

23.4: Leaves

• Gas exchange and homeostasis
• Stomata allow air to pass
• Plants maintain homeostasis by keeping their stomata open allowing photosynthesis to take place but not so much to lose excessive amounts of water
• Guard cells close when water pressure inside the guard cells decrease and open when water pressure inside the cell is high. If the plant has plenty of water, the guard cells are open allowing gases through and also transpiration. Too much water loss lowers the water pressure inside the cells causing them to close.

23.5: Transport in Plants

• Water transport
• Water pressure from water entering cells is not enough to transport water much against the force of gravity. Bryophytes are short for a reason.
• Other forces must be in play because trees grow to great heights. How does water get from the roots of tall trees to the leaves high above the ground?

23.5: Transport in Plants

• Transpiration - The evaporation of water from leaves is the main force carrying water in plants.
• As the water evaporates from leaves, the drying cell walls draw water from xylem tissues which draw water from the vascular system throughout the plant.
• The process relies on the physical characteristics of the vascular system and individual water molecules.

23.5: Transport in Plants - Water

• There are two forces of attraction
• Cohesion (attraction between like molecules) between water molecules and
• Adhesion (attraction between unlike molecules) between water molecules and the plant’s vascular system.
• The tendency of water to rise in a thin tube is capillary action

23.5: Transport in Plants - Nutrients

• How does material flow through phloem?
• Active transport moves sugars into sieve tubes
• Water moves into the tube via osmosis
• Sugars are actively pumped out of sieve tubes to regions of the plant needing them. (Think: maple syrup)

24: Plant Reproduction and Response

24.1: Reproduction in flowering plants

24.2: Fruits and Seeds

24.3: Plant hormones

24.4: Plants and Humans

24.1: Reproduction in Flowering Plants

• The structure of flowers
• Flowers are composed of four different kinds of specialized leaves
• Sepals, petals: The outermost parts of the flower
• Stamens: The male parts of the flower. Stamens consist of a stalk (a filament) tipped by an anther that produces pollen grains
• Carpels: The innermost part of the flower. Carpels produce and shelter the female gametophytes and, later, seeds. The carpel narrows to a stalk (style) topped by a stigma which captures pollen. A single carpel or several fused carpels is called a pistil.

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24.1: Reproduction in Flowering Plants

24.1: Reproduction in Flowering Plants: Life cycle

• Development of male gametophytes
• Pollen (male gametophytes) develop inside anthers
• Meiosis produces four haploid spore cells
• Each spore divides to produce 2 haploid nuclei in one pollen grain
• The two nuclei are surrounded by a protective thick wall until the pollen lands on a stigma

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24.1: Reproduction in Flowering Plants: Life cycle

24.1: Reproduction in Flowering Plants: Life cycle

• Development of female gametophytes
• Female gametophytes develop inside the carpel
• A single diploid cell undergoes meiosis to produce four haploid cells, three of these disintegrate
• The remaining cell divides producing 8 nuclei. These 8 nuclei and the surrounding membrane are called the embryo sac
• The sac contained within the ovule makes up the female gametophyte

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24.1: Reproduction in Flowering Plants: Life cycle

24.1: Reproduction in Flowering Plants: Life cycle

• Fertilization
• When a pollen grain lands on the stigma of a flower of the same species, it grows a pollen tube
• Of the pollen grains two cells . . .
• One divides and forms two sperm cells
• The other cell becomes the pollen tube containing the two sperm cells
• The pollen tube grows into the style where it reaches the ovary and enters an ovule

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24.1: Reproduction in Flowering Plants: Life cycle

• Fertilization
• Inside the embryo sac a double fertilization takes place
• One sperm cell fuses with the egg to produce a diploid zygote which grows into the plant embryo
• The second sperm cell fuses with two polar nuclei to form a triploid (3N) cell. The cell grows into the food rich tissue endosperm which nourishes the seedling as it grows

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24.1: Reproduction in Flowering Plants: Life cycle

• Corn seed
• The embryo uses to stored food to grow until it can provide for itself through photosynthesis

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What is the advantage of double fertilization?

24.1: Reproduction in Flowering Plants: Life cycle

• Vegetative reproduction
• Asexual reproduction
• A plant can reproduce vegetatively very quickly and can cover a large area in a little amount of time.
• Sumac stands along roadsides
• Aspen forests are the vegetative extensions of one or a few original plants
• No increase in genetic variability
• Grafting and cuttings are methods humans use to propagate new plants

24.2: Fruit and Seeds

• As angiosperm seeds mature, ovary walls thicken to form a fruit the encloses the developing seeds.
• Fruits are not intended to nourish the plant embryo
• Fruits are eaten by a wide range of animals that digest the fruit but not the seeds. The seeds pass through the animal’s digestive system and are passed with feces
• Dry fruits are designed to be carried by other means
• “Stick tights”
• Dandelion parachutes
• Maple “helicopters”

24.2: Fruit and Seeds

• Some seeds require a period of dormancy before they sprout. Others will sprout soon after maturing
• Germination is the resumption of growth of the plant embryo
• Seeds absorb water causing the food-storing tissue to swell and crack open the seed coat
• The root appears first then the shoot
• Cotyledons are the plant’s first leaves and contain nutrients. Some cotyledons stay below ground and others are above ground
• Some seeds will germinate only after catastrophes such as wild fire (jack pine)

24.3: Plant hormones

• Plant Hormones are chemical signals that affect the growth, activity, and development of cells, tissues, and organs
• The hormones produced by a mature flower inhibits the growth of flower buds on a different part of the plant.
• When the mature flower is done blooming the hormone stops being produced and the young bud can mature

24.3: Plant hormones

• Hormones act on target cells
• The target cell must have hormone receptors to which the hormone can bind
• Cells without receptor proteins are unaffected by hormones
• A hormone may affect different cells on the same plant in different ways
• Auxins stimulate cell elongation and the growth of new roots
• Auxins are produced in the apical meristem and are transported throughout the plant

24.3: Plant hormones

• One of the effects of auxins is to stimulate cell elongation
• Auxins collect in the shaded part of the shoot which causes the cells on the dark side of the shoot to grow longer - causing the shoot to bend toward the light.

24.3: Plant hormones

• Auxins also regulate branching in meristems
• Lateral buds is inhibited by auxins
• The closer a lateral bud is to the apex of the shoot it is inhibited more
• This is called apical dominance
• Cytokinins are hormones produced in growing roots, developing fruits and seeds
• They stimulate cell division

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24.3: Plant hormones

• Gibberellins stimulate growth
• Abscisic acid inhibits cell division
• Gibberellins and abscisic acid have opposite effects, much like auxins and cytokinins
• The opposing effects of plant hormones contribute to the balance necessary for homeostasis.
• Ethylene, a plant hormone, is actually a gas. Fruits tissues release ethylene gas that stimulate fruits to ripen. Causes plants to seal off and drop unnecessary organs such as leaves or fruit.

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24.3: Tropisms

• Growth responses to the environment are tropisms
• Tropisms are responses to light, gravity, and touch
• Response to light is phototropism due to auxin levels
• Response to gravity is gravitropism. Auxins migrate to the lower sides of horizontal roots and stems. Horizontal stems bend upright and roots bend down.
• Response to touch is thigmotropism. Vines and climbing plants respond to touching objects by wrapping tightly to the object. Venus flytraps close when insects trigger sensory cells on the inside of the leaf

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24.3: Tropisms

24.3: Response to Seasons

• Photoperiod and Flowering
• Many plants respond to changing periods of light and darkness
• This response is photoperiodism and is a major factor in the timing of seasonal activities such as flowering and growth
• A plant pigment, phytochrome, is responsible for these responses
• Winter dormancy
• Phytochrome also plays a role as plants prepare for winter
• Deciduous plants turn off photosynthetic pathways, transport materials from leaves to roots, and seal leaves off from the rest of the plant