Feralis Ch 2 Flashcards
2 criteria in determining the living vs non-living
- Independent metabolism (Viruses lack this and are not considered alive)
- Ability to self-replicate
Species name
Italicized, consists of a genus name and a species name.
Taxonomic ranks, from most general to specific
Kingdom, phylum, class, order, family, genus, species.
Taxonomic levels for humans
Domain: Eukarya Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Class: Mammalia Order: Primata Family: Hominidae Genus: Homo Species: Sapiens
Systematics
Study of evolutionary relationships among organisms
Eukaryote Vs. Prokaryote
The two major divisions in living organisms.
Eukaryotic chromosomes contain long, linear DNA with histones that is enclosed in a nucleus. They have specialized organelles to isolate metabolic activities. The flagella and cilia microtubules are arranged in a 9+2 array.
Prokaryotic cells have a single chromosome that is short. They have circular DNA that usually does not have histones. The exception are archaea that have histones. Prokaryotes may contain plasmids. The flagella consist of chains of the protein flagellin instead of the 9 + 2 microtubule arrangement seen in eukaryotic cells. Uses proton motive force to spin and give locomotion in bacteria (electrical gradient), not ATP!
Autotrophs
Manufacture their own organic materials. They use light (photo) or chemicals (chemo) such as H2S, NH3, NO, and NO3
Heterotrophs
Obtain energy by consuming organic substances produced by autotrophs.
Parasites and saprobes (saprophytes)
Parasites
A heterotroph. Obtain energy from living tissues of hosts
Saprobes (saprophytes)
A heterotroph. Obtain
energy and feed from dead, decaying matter which contribute to organic decay. Decomposers are slightly different in that they break down dead and decaying matter
Obligate aerobes
must have O2 to live
Obligate anaerobes
Require absence of O2 to live; they cannot live with the presence of oxygen. They are unable to detoxify some products of oxygen metabolism, e.g. H2O2 would be toxic to them
Facultative anaerobe
Grows in the presence of O2, but can switch to anaerobic metabolism when O2 is absent. Prefer to grow in the presence of oxygen if possible because respiration is more efficient and produces more ATP.
Domain Archaea
Prokaryotes, non-pathogenic. Cell walls contain various polysaccharides, but they do not contain peptidoglycan as seen in bacteria. Cell walls also contain cellulose or chitin. Phospholipid membrane contains glycerol, but the glycerol is an isomer of the one used in bacteria and eukaryotes. Hydrocarbon chain in is branched with ether-linkages
Archaea and eukaryote similarities
- DNA of both archaea and eukaryotes are associated with histones, unlike bacterial DNA
- Ribosome activity is not inhibited by antibiotics streptomycin and chloramphenicol, unlike bacteria
Methanogens
A group of archaea. These are obligate anaerobes that
produce CH4 as a by-product of obtaining energy from H2 to fix CO2
Extremophiles
A group of archaea. They live in extreme environments. Consists of Halophiles (salt lover), Thermophiles (heat lover), and Other extremophiles
Halophiles
An extremophile, which is a group of archaea. They live in high salt concentration environments. Most are aerobic and heterotrophic; others are anaerobic and photosynthetic with the pigment bacteriorhodopsin
Thermophiles
An extremophile, which is a group of archaea. Are sulfur-based chemoautotrophs that live in very hot places. Can produce bright colours.
Other extremophiles
An extremophile, which is a group of archaea. Live in high acid/base/pressure environments
Domain Bacteria (Five Kingdoms)
Cell walls that have peptidoglycan, which is a polymer of monosaccharides with amino acids. DNA is not associated with histones, and ribosome activity is inhibited by antibiotics like streptomycin and chloramphenicol
Classification of bacteria
- Mode of nutrition/how they metabolize resources
- Ability to produce endospores (resistant bodies that contain DNA and small amounts of cytoplasm surrounded by a durable wall)
- Means of motility - flagella, corkscrew motion, or gliding through slime material
- Shapes - cocci (spherical), bacilli (rod- shaped), spirilla/spirochetes (spirals)
- Peptidoglycan cell wall - gram-positive bacteria have thick peptidoglycan cell walls. Gram-negative bacteria have thin peptidoglycan covered with lipopolysaccharides. Peptidoglycan contains amino sugars
i. Teichoic acids - these acids on the cell walls of bacterium are used as recognition and binding sites by bacterial viruses that cause infections. Teichoic acids also provide cell wall rigidity and are only found on gram-positive bacteria! Teichoic acids are covalently attached to the peptidoglycan layer
Common groups of bacteria
Cyanobacteria, Chemosynthetic, Nitrogen-fixing, Spirochetes
Cyanobacteria
A common group of bacteria. They are
photosynthetic and contain an accessory pigment called phycobilins. Some have specialized cells called heterocysts that produce nitrogen-fixing enzymes; These enzymes convert fixed inorganic nitrogen gas into NH3 that can be used to make amino acids and nucleotides. Cyanobacteria are known as blue-green algae and are not related to the other eukaryotic algae groups. They are the oldest known fossils and can rapidly grow in aquatic environments, turning the water green or blue-green
Chemosynthetic
A common group of bacteria. These bacteria are autotrophs. Some are nitrifying bacteria, which are able to convert ammonia to nitrate
Nitrogen-fixing
A common group of bacteria. These bacteria are heterotrophs that fix N2. They live in the nodules of plants, and this is a form of mutualism because the bacteria provides useable nitrogen for the plant, while the plant gives the bacteria a home and fixed carbon to utilize
Spirochetes
A common group of bacteria. These are coiled bacteria that move with a corkscrew motion. There is internal flagella between cell wall layers
Kingdom Monera
DAT Pro-Tip: Some classifications use the Kingdom Monera, rather than using domains, for archaea and bacteria.
Domain Eukarya (4 Kingdoms)
Kingdoms are protista, fungi, plantae, animalia
Kingdom Protista
Domain Eukarya. This is an artificial kingdom used mainly for convenience and is poorly understood. Features shared by two or more groups may represent convergent evolution, and most protists are unicellular. They are generally classified by means of locomotion, and all protists live in moist environments.
- Algaelike
- Protozoa
- Fungus-like
Algaelike (plant-like)
Domain Eukarya. Kingdom Protista. These protists all obtain energy by photosynthesis. All have chlorophyll a, and some have accessory pigments. Mainly categorized by the form of carbohydrate used to store energy, the number of flagella, and the makeup of the cell wall
i. euglenoids
ii. dinoflagellates
iii. diatoms
iv. brown algae
v. rhodophyta
vi. chlorophyta
Euglenoids
Domain Eukarya. Kingdom Protista. Under algaelike (plant-like).
Have 1-3 flagella at apical end. Instead of cellulose cell wall, euglenoids have thin, protein strips called pellicles that wrap over cell membranes. They are heterotrophic in the absence of light, and some have eyespots that permit phototaxis. They live in fresh water. They lack cell walls and are highly motile, so they are arguably animal-like too
Dinoflagellates
Domain Eukarya. Kingdom Protista. Under algaelike (plant-like).
Have 2 flagella. One flagellum is posterior, while the second flagellum is transverse and rests encircling the mid-groove perpendicular to the first flagellum. Some are bioluminescent. Others produce nerve toxin that concentrates in filter-feeding shellfish, which can cause illness to humans when eaten. Dinoflagellates are responsible for the algal bloom known as red tide: high concentrations of algae that can lead to toxin buildup, depletion of dissolved oxygen, and other harmful effects
Diatoms
Domain Eukarya. Kingdom Protista. Under algaelike (plant-like).
Have tests (shells) that fit together like a box with a lid. They also contain SiO2 (silica)
Brown algae
Domain Eukarya. Kingdom Protista. Under algaelike (plant-like).
Are multicellular and flagellated sperm cells. They look like giant seaweed
Rhodophyta
Domain Eukarya. Kingdom Protista. Under algaelike (plant-like).
Are red algae and have red accessory pigments called phycobilins. They are multicellular and their gametes do not have flagella
Chlorophyta
Domain Eukarya. Kingdom Protista. Under algaelike (plant-like).
Are green algae and have both chlorophyll a and b. Have cellulose in cell walls, and they store energy in the form of starch. Some species have isogamous gametes (both sperm and egg are equal in size and motile), some are anisogamous (sperm and egg differ in size), and others can be oogamous (large egg cell remains with the parent and is fertilized by small, motile sperm). There is a trend from unicellular organisms (Chlamydomonas) towards multi-cellular colonies (Gonium, Pandorina, Volvox). A lineage of Chlorophytes called charophytes are believed to be the ancestor of plants. Spirogyra are a green algae as well
Protozoa (animal-like)
Domain Eukarya. Kingdom Protista. These protists are heterotrophs. They consume living cells or dead organic matter, and are unicellular eukaryotes.
i. rhizopoda
ii. foraminifera
iii. apicomplexans
iv. ciliates
v. amoebas
Rhizopoda
Domain Eukarya. Kingdom Protista. Under protozoa (animal-like).
Are amoebas that move by extensions of their cell body called pseudopodia. They encircle their food using phagocytosis.
Foraminifera
Domain Eukarya. Kingdom Protista. Under protozoa (animal-like).
aka forams, have tests (shells) usually made of calcium carbonate. Sediments of foraminifera indicate oil deposits
Apicomplexans
Domain Eukarya. Kingdom Protista. Under protozoa (animal-like).
Are parasites of animals. They have an apical complex (complex of organelles located at an end of the cell) and no physical motility. They form spores which are dispersed by hosts that complete their life cycle. Malaria is caused by a sporozoan
Ciliates
Domain Eukarya. Kingdom Protista. Under protozoa (animal-like).
Use cilia for moving and other functions. They have specialized structures: mouths, pores, contractile vacuoles [H2O balance], two kinds of nuclei (large macronucleus and several small nuclei). They are the most complex of all cells. An example of a ciliate is the paramecium.
Amoebas
Domain Eukarya. Kingdom Protista. Under protozoa (animal-like).
Are a genus of protozoa, and are shapeless and unicellular. They move via pseudopods
Fungus-like protists
Domain Eukarya. Kingdom Protista. Resemble fungi and form filaments/spore-beating bodies like fungi do
i. Cellular slime molds
ii. Plasmodial slime molds
iii. Oomycota
Cellular slime molds
Domain Eukarya. Kingdom Protista. Under fungus-like protists.
Have fungus-like and protozoa-like characteristics. The spores germinate into amoebas which feed on bacteria. When no food is available, amoebas aggregate into a single unit slug. The individual cells of the slug mobilize into a stalk with a capsule at the top to release spores which germinate and repeat the cycle. Their stimulus for aggregation is cAMP secretion, which is secreted by the amoebas that first experience food deprivation
Plasmodial slime molds
Domain Eukarya. Kingdom Protista. Under fungus-like protists.
Grow as a single, spreading mass (plasmodium) that feeds on decaying vegetation. When there is no food or desiccation occurs, stalks ‘bearing spore capsules’ form and ‘haploid spores’ released from the capsules germinate into haploid amoeboid/flagellated cells. These cells fuse to form diploid cells and grow into plasmodium but are not mutualistic with others.
What is the difference between plasmodial and cellular slime molds? Both have a stalk and release haploid spores which haploid amoeba cells emerge from. In plasmodial slime molds, the amoeboid cells fuse and form a diploid zygote. The zygotes’ nuclei divide but not the cytoplasm, giving a large multinucleate feeding stage; this is the plasmodium stage – not to be confused with genus Plasmodium of malaria. When conditions become harsh, the plasmodium erects a stalk with fruiting bodies called
sporangia. Inside the sporangia, cells go through meiosis and haploid spores are released. In cellular slime molds, the amoeboid cells feed on bacterium on their own, and reproduce asexually via mitosis. They can reproduce sexually and form a zygote, but the zygote just ends up going through meiosis and releasing new haploid amoeba cells anyway. When conditions get harsh, the individual haploid cells aggregate but do not fuse, forming the slug-like aggregate of many haploid cells. It migrates, stops, forms stalk with asexual fruiting body, and haploid spores get released
Oomycota
Domain Eukarya. Kingdom Protista. Under fungus-like protists.
Are water molds, mildews, and white rusts. They are either parasites or saprobes, which receives nutrition from dead and decaying organic matter. Forms filaments called hyphae, which secrete enzymes that digest surrounding substances like fungi do. Hyphae lacks septa (cross wall) which is present in true fungi that partition filaments into compartments. Thus, they are coenocytic because they lack septa and contain many nuclei within a single cell. The cell walls are made of cellulose rather than the chitin that is seen in true fungi
Kingdom Fungi
Domain Eukarya. Fungi grow as filaments called hyphae, and mycelium is a mass of hyphae. Cell walls contain chitin (N- containing polysaccharide). Some fungi have septum which divide filaments into compartments containing a single nucleus. Fungi without septa are coenocytic, meaning they are multi-nucleate. Fungi are eukaryotic heterotrophs. They secrete digestive enzymes and then absorb the products of digestion. Fungi can reproduce sexually or asexually. They can also alternate their diploid/haploid stages, but the haploid stage generally predominates in the life cycle of most fungi. Fungi are generally immotile, and can attack living or dead matter. They are more similar to human cells than bacterial cells. Fungi are generally classified into divisions based on the type of sexual spores they produce; if there is no sexual phase, they are called ‘imperfect fungi’. Yeast is a broad class of unicellular fungi, so not all fungi are multicellular. The main purpose of fungi is decomposition and to break down lots of biological waste. However, some fungi can be parasitic. These parasitic fungi have hyphae called haustoria that can penetrate the host.
- Stages of fungi sexual reproduction
- Means of asexual reproduction
- Six fungus groups
- Miscellaneous fungal genus
Stages of fungi sexual reproduction
Fungi are primarily haploid but form temporary diploid structures for sexual reproduction. Steps are plasmogamy, karyogamy, and meiosis.
Plasmogamy
Step 1/3 of fungi sexual reproduction.
Fusing of cytoplasm of cells from 2 different fungal strains to produce a single cell without fusing of the nuclei. The resulting cell has a pair of haploid nuclei, one from each strain and is now called a dikaryon. Dikaryotic hypha is hypha containing dikaryon
Karyogamy
Step 2/3 of fungi sexual reproduction.
Fusing of 2 haploid nuclei of a dikaryon to form a single diploid nucleus
Meiosis
Step 3/3 of fungi sexual reproduction.
Meiosis of diploid nucleus restores haploid condition. The daughter cells develop into haploid spores which germinate into haploid hyphae (has 1 fungal strain) and then merge into dikaryons to repeat the cycle
Means of asexual reproduction
Domain Eukarya. Kingdom Fungi. There are a few methods of fungi asexual reproduction which include fragmentation (breaking up hyphae), budding (small hyphae outgrowth), and asexual spores, further described as two types:
i. Sporangiospores
ii. Conidia
Sporangiospores
Domain Eukarya. Kingdom Fungi. Asexual spore type. Spores produced in sac-like capsules called sporangia that are each borne on a stalk called a sporangiophore
Conidia
Domain Eukarya. Kingdom Fungi. Asexual spore type. A type of asexual spore formed at the tips of specialized hyphae and are not enclosed inside sacs. Hyphae bearing conidia are called conidiophores
Six fungus groups
Domain Eukarya. Kingdom Fungi.
Group names with the suffix –mycota denote a division. Group names with the suffix –mycete denote classes. Both suffixes are used interchangeably.
i. Zygomycota
ii. Glomeromycota
iii. Ascomycota
iv. Basidomycota
v. Deuteromycota
vi. Lichens
Zygomycota
Domain Eukarya. Kingdom Fungi. One of six fungus groups.
They lack septa except the filaments bordering reproductive filaments. They reproduce sexually by fusion of hyphae from different strains, followed by plasmogamy, karyogamy, and meiosis. Haploid zygospores are produced, then germinate into new hyphae (e.g. bread molds). They reproduce asexually via sporangia
Glomeromycota
Domain Eukarya. Kingdom Fungi. One of six fungus groups.
These fungi lack septa and do not produce zygospores. They form mutualistic associations with roots of plants, and this relationship is called a mycorrhiza. In this relationship, plants provide carbohydrates, and the fungus increases the ability of the plant to absorb nutrients, especially phosphorus
Ascomycota
Domain Eukarya. Kingdom Fungi. One of six fungus groups.
These fungi have septa and reproduce sexually by producing haploid ascospores. After plasmogamy of hyphae from different strains occurs, dikaryotic hypha produces more filaments by mitosis. Karyogamy and meiosis occurs in terminal hyphal which leads to 4 haploid cells, and then mitosis leads to producing 8 haploid ascospores in a sac called an ascus. The ascus can be located within an ascocarp. Ascocarps are cup-shaped fruiting bodies. The spores release and germinate into hyphae, and the cycle repeats
Basidiomycota
Domain Eukarya. Kingdom Fungi. One of six fungus groups.
They have septa and reproduce sexually by producing haploid basidiospores. They go through plasmogamy and mitosis, which leads to the creation of a fruiting body called the basidiocarp such as mushrooms. Karyogamy occurs in terminal hyphal cells called basidia, followed by meiosis to produce 4 haploid basidiospores. They can reproduce asexually, and less commonly via conidia
Deuteromycota
Domain Eukarya. Kingdom Fungi. One of six fungus groups.
They are imperfect fungi and an artificial group because they have no known sexual reproductive cycle. Penicillium produces penicillin, which is an antibiotic that disrupts bacteria’s ability to synthesize its cell wall
Lichens
Domain Eukarya. Kingdom Fungi. One of six fungus groups.
Are symbiotic associations between fungi and algae or cyanobacteria. The fungi receives carbohydrates produced by the algae or cyanobacteria via photosynthesis. The fungi can also provide nitrogen if the algae is nitrogen-fixing. The fungus, usually ascomycete, provides water and protection from the environment and UV light for the algae or cyanobacteria. The fungi can also produce toxic chemicals to protect against grazers
Miscellaneous Fungal Genus
Domain Eukarya. Kingdom Fungi.
i. Rhizopus
ii. Candida
iii. Saccharomyces cerevisiae
Rhizopus
Domain Eukarya. Kingdom Fungi. Under miscellaneous fungal genus
A fungal pathogen that
is involved with food spoilage. It is an obligate parasite because it depends on its host for survival. Rhizopus stolonifer is commonly known as the black bread mold, and is also a type of Zygomycota
Candida
Domain Eukarya. Kingdom Fungi. Under miscellaneous fungal genus
Is involved in infections of mucous membranes
Saccharomyces cerevisiae
Domain Eukarya. Kingdom Fungi. Under miscellaneous fungal genus
A type of yeast that is involved in fermenting sugars to alcohol
Kingdom Plantae
Domain Eukarya
- Adaptations for survival on land
- Major seedless plant divisions
- Seeded vascular plant divisions
Adaptations for survival on land
Domain Eukarya. Kingdom Plantae.
i. dominant diploid generation
ii. cuticle
iii. vascular system
iv. sperm dispersla
v. anthrophyta
vi. seasonal variations
Dominant diploid generation
Domain Eukarya. Kingdom Plantae. Under adaptations for survival on land.
The dominant generation in plants is the diploid sporophyte generation except in primitive bryophytes which include mosses, liverworts, and hornworts. A diploid organism provides 2 copies of DNA that protects plants against genetic damage that they were more susceptible to once out of the water
Cuticle
Domain Eukarya. Kingdom Plantae. Under adaptations for survival on land.
A waxy covering that reduces desiccation (drying up/ water loss)
Vascular system
Domain Eukarya. Kingdom Plantae. Under adaptations for survival on land.
Having a vascular system reduces the plant’s dependency on water, meaning the cells no longer need to be close to water. This led to the formation of specialized tissues: true leaves (centers for photosynthesis), true stems (supports the leaves), true roots (acquires water/anchors plant). Two groups of vascular tissues that exist within plants evolved: xylem (transports water) and phloem (transports sugar)
Sperm dispersal
Domain Eukarya. Kingdom Plantae. Under adaptations for survival on land.
In primitive plant divisions, they use flagellated sperm which requires water to swim to eggs. In advanced plant divisions such as the coniferophyta and anthophyta, the sperm is packaged as pollen and dispersed with wind
Anthrophyta
Domain Eukarya. Kingdom Plantae. Under adaptations for survival on land.
A division of plants otherwise known as angiosperms or flowering plants. They have their gametophytes enclosed and protected inside an ovary
Seasonal variations
Domain Eukarya. Kingdom Plantae. Under adaptations for survival on land.
In coniferophyta and anthophyta, they express seasonal variations in response to the availability of water and light. Some are deciduous, meaning they shed their leaves to prevent water loss through slow- growing seasons. Others like desert plants will germinate, grow, flower, and produce seeds rapidly in brief periods of rain
Major seedless plant divisions
Domain Eukarya. Kingdom Plantae.
All plant divisions, including the seeded plants, are vascular except for the bryophytes. Vascular plants are called tracheophytes and have true roots, leaves, and stems. Tracheophytes also have germination of antheridium and archegonium that will produce diploid zygotes that become a sporophyte, which is also the dominant generation
i. Bryophytes
ii. Lycophyta
iii. Pterophyta
Bryophytes
Domain Eukarya. Kingdom Plantae. Under major seedless plant divisions.
This division includes the mosses, liverworts, and hornworts. Gametes are produced in gametangia (protective structures) on gametophytes. They have a haploid dominant stage in their life cycle. The antheridium is the male gametangium which produces flagellated sperm that swim through water. The archegonium is the female gametangium which produces eggs. The zygote grows into a diploid structure called the sporophyte, but it is still connected to the gametophyte. In mosses, the sporophyte structure is a stalk bearing capsule which contains haploid spores produced by meiosis. The spores are dispersed by wind and germinate into haploid gametophytes which then produces the antheridium and archegonium.
These plants are anchored to the substrate by rhizoids rather than roots. Rhizoids are root-like absorptive structures. Bryophytes lack true roots, true leaves, and true stems meaning they subsequently lack vascular tissues, and so they must remain in/near water. Algae and some fungi form rhizoids as well.
Lycophyta
Domain Eukarya. Kingdom Plantae. Under major seedless plant divisions.
Includes club mosses, spike mosses, and quillworts, which are herbaceous. Club and spike mosses produce clusters of spore- bearing sporangia in cone-like structures called strobili. A type of lycophyte called the resurrection plant, a spike moss, can recover from a dead-like appearance after it is watered
Pterophyta
Domain Eukarya. Kingdom Plantae. Under major seedless plant divisions.
3 groups: ferns, horsetails, and whisk ferns. The life cycle in PDF is for ferns, but it is very similar for lycophyta as well. The primary difference is that the lycophytes use a prominent cone- like strobili, but ferns use the sori on the undersurface of their leaves. Sori are clusters of sporangia on in pterophytes.
Ferns
Domain Eukarya. Kingdom Plantae. Under major seedless plant divisions. Under pterophyta.
Produce clusters of
sporangia (structures in which spores are produced) called sori that develop on the undersurface of fern fronds. In ferns, the predominant plant form is the sporophyte
Horsetails
Domain Eukarya. Kingdom Plantae. Under major seedless plant divisions. Under pterophyta.
These include extinct woody trees. The stems of horsetails are hollow, ribbed, and are jointed at nodes. The strobili bear spores. Stems, branches, and leaves are green and thus are photosynthetic. The plants also have a rough texture due to silica
Whisk ferns
Domain Eukarya. Kingdom Plantae. Under major seedless plant divisions. Under pterophyta.
These plants have branching stems without roots. The leaves are reduced to small appendages or are absent. The absence of roots and leaves is considered secondary loss, which means they were lost as whisk ferns diverged from their ancestors
Seeded vascular plant divisions
Domain Eukarya. Kingdom Plantae.
The next two plant divisions produce seeds: male spores and female spores. Microsporangia produces microspores (male spores) and megasporangia produces the megaspores (female spores).
2 plant divisions of the seeded vascular plants:
i. Coniferophyta
ii. Anthophyta (angiosperms)
Microsporangium
Domain Eukarya. Kingdom Plantae. Under seeded vascular plant divisions.
Produces numerous microspore mother cells, which divide by meiosis to produce four haploid cells a.k.a. microspores. These microspores then mature into pollen grains which represent the gametophyte generation. Pollen grains are the immature male gametophyte with a hard covering. The grains further divide into three cells (in flowering plants) or four cells (in conifers). One of the cells is a vegetative/tube cell that controls the growth of the pollen tube, while the other cells are sperm cells
Megasporangium
Domain Eukarya. Kingdom Plantae. Under seeded vascular plant divisions.
The nucellus produces the megaspore mother cell. After undergoing meiosis, four haploid cells are created but only one survives to become the megaspore (female gametophyte generation). That megaspore undergoes mitosis to produce the embryo sac. There is one egg in flowering plants and two eggs in conifers. One or two tissue layers called integuments surround the megasporangium. The ovule consists of the integument, nucellus, and megaspore daughter cells. The micropyle is the opening within the integuments for pollen to access to the egg
Remember that it is the seeds and not the spores directly that are the dispersal unit.
Once the pollen grain contacts the megasporangium, the tube cell of the sperm directs the growth of the pollen tube through the micropyle and towards the egg. Fertilization and the creation of a zygote occurs, which becomes an embryo. This is the beginning of the sporophyte generation. The integuments become the seed coat.
Coniferophyta
Domain Eukarya. Kingdom Plantae. Under seeded vascular plant divisions.
a.k.a. gymnosperms meaning naked-seeds. These plants are cone-bearing and include the pines, firs, spruces, junipers, redwoods, and cedars. They have pollen-bearing male cones and ovule-bearing female cones. The seeds produced in unprotected megaspores are near the surface of the reproductive structure. Fertilization and seed development are lengthy, requiring one to three years
Anthophyta (angiosperms)
Domain Eukarya. Kingdom Plantae. Under seeded vascular plant divisions.
These are flowering plants which include fruits, maple, oaks, grass, etc., and are the dominant land plant form. The flower is the reproductive structure of an angiosperm.
Angiosperms have major evolutionary advancements due to their structure. They can attract pollinators such as insects and birds. The ovule is protected inside an ovary which develops into fruit following fertilization. The seeds are then dispersed by wind or by other animals.
Major parts of the flower of an angiosperm
Domain Eukarya. Kingdom Plantae. Under seeded vascular plant divisions.
Pistil, stamen, petals
Pistil
Domain Eukarya. Kingdom Plantae. Under seeded vascular plant divisions. Major parts of the flower of an angiosperm
The female reproductive structure. It has three parts: ovary (egg-bearing), style, and stigma. The ovary encloses one or more ovules with a monopoloid egg nucleus
Stamen
Domain Eukarya. Kingdom Plantae. Under seeded vascular plant divisions. Major parts of the flower of an angiosperm
The male reproductive structure. It has a pollen-bearing anther, stalk, and filament. The anther is the chamber where the pollen develops
Petals
Domain Eukarya. Kingdom Plantae. Under seeded vascular plant divisions. Major parts of the flower of an angiosperm
The petal, and sometimes the sepals too, function to attract pollinators. In angiosperms, the sepal encloses and protects the flower bud
Angiosperm process of fertilization step 1/3
Domain Eukarya. Kingdom Plantae. Under seeded vascular plant divisions.
The pollen lands on the sticky stigma. The pollen tube (elongating cell) that contains the vegetative nucleus grows down the style toward the ovule. There are 2 sperm cells inside the pollen tube.
Angiosperm process of fertilization step 2/3
Domain Eukarya. Kingdom Plantae. Under seeded vascular plant divisions.
The ovule within the ovary consists of a megaspore mother cell surrounded by the nucellus and integuments. The megaspore mother cell undergoes meiosis to form four haploid megaspores. One of those megaspores survives and undergoes mitosis three times to create eight nuclei. Six of those nuclei undergo cytokinesis and form plasma membranes (embryo sac). At the micropyle end of the embryo sac are three cells consisting of an egg and two synergids. At the other end of micropyle are three antipodal cells. In the middle are polar nuclei which are two haploid cells
Angiosperm process of fertilization step 3/3
Domain Eukarya. Kingdom Plantae. Under seeded vascular plant divisions.
Pollen tube (two sperm cells) enters the embryo sac through the micropyle. One sperm cell fertilizes the egg and forms the diploid zygote. The nucleus of the second sperm cell fuses with both polar nuclei to create a triploid (3n) nucleus and endosperm, which provides nutrients. Double fertilization is fertilization of the egg and polar nuclei each by a separate sperm cell– this is unique to angiosperms!
Kingdom Animalia
This kingdom is monophyletic meaning all the species can be traced back to one common ancestor. Its members do share these common characteristics:
• Multicellular
• Heterotrophic
• Dominant diploid generation
• Motile at some part of their life cycle
• 2-3 layers of tissues form during embryonic development
Body symmetry in kingdom animalia
Animals can have different types of symmetry. Radial symmetry means the organisms have a top and bottom but no distinct left and right sides; they have circular body patterns. Animals with bilateral symmetry have a distinct left and right side. When divided by a sagittal plane, the left and right sides are mirror images. Organisms with bilateral symmetries can be described with these anatomical phrases: dorsal-top, ventral- bottom, anterior-towards the head, posterior-towards the tail. There are also organisms that are completely asymmetrical.
Cephalization in kingdom animalia
In animals with bilateral symmetry, they can have a higher concentration of nerve tissue located at the anterior end as organisms increase in complexity. E.g. brains are highly developed and have sensory organs
Gastrovascular cavity in kingdom animalia
This is the digestive system. Gastrovascular cavities have one opening and is sac-like with limited processes. A digestive tract has two openings with specialized activities as food travels through
Tissue complexity in kingdom animalia
Eumetazoans are organisms with true tissues that are organized into germ layers. Diploblastic organisms have two embryonic cell layers. Triploblastic organisms have three embryonic cell layers, which from superficial to deep are called the ectoderm, the mesoderm, and the endoderm. Another group are the parazoans. Parazoans do not have organized true tissues, and thus organs do not develop
Coelom in kingdom animalia
Animals can be classified as either acoelomate, pseudoceolomate, or coelomate. The coelom is derived from the mesoderm, and is a fluid-filled cavity that cushions the internal organs. Acoelomates lack a coelom. Pseudocoelomates have a cavity, but it is not completely lined by mesoderm- derived tissue
Segmentation in kingdom animalia
Some organisms have segmented body structures. The segmentation can be repetitive or is sometimes specialized. Segmentation can be seen in arthropods, annelids, and chordates
Protostomes and deuterostomes in kingdom animalia
Cleavages/cell divisions in a zygote’s early development is different depending on the type of organism. The archenteron is the primitive gut that forms during gastrulation in the developing blastula. It develops into the digestive tract of an animal, and its opening will then develop into the mouth or the anus depending on the type of organism. Protostomes are organisms that develop mouth first, and deuterostomes are organisms that develop anus first. The coelom will either develop from the splitting of the mesodermal tissue at the sides of the archenteron or directly from an out- pouching in the archenteron wall.
Porifera phylum
Domain Eukarya. Kingdom Animalia.
Otherwise known as sea sponges, these organisms are parazoans. They feed by filtering water through the sponge wall of flagellated cells called choanocytes. The flagellum of choanocytes creates a flow of water for filter feeding. Water exits through the osculum opening. Choanocytes pass food to amoebocytes for digestion and distribution of nutrients. An amoebocyte is a mobile cell in the body of invertebrates which can engulf food. These cells move by pseudopodia, which is a temporary protrusion of the cytoplasm-actin of an amoeba. The sponge wall contains spicules, which are skeletal needles made from CaCO3 or SiO2. Sea sponges are sessile, meaning they cannot move. Porifera are used in the development and research of antibiotics
Cnidaria phylum
Domain Eukarya. Kingdom Animalia.
These include the hydrozoans, jellyfish, sea anemones, and corals. Cnidarians have two body forms: the floating, umbrella-shaped body with tentacles called the medusa, and the sessile cylinder-shaped body with rising tentacles called the polyp. Some cnidarians alternate between the medusa and polyp forms in their life cycle. Cnidoblasts, which become cnidocytes, are specialized cells located in the tentacles and body walls of cnidarians. The interior of the cnidoblasts are filled with stinging organelles called nematocysts. An obsolete term for this group is the coelenterates. Cnidarians are carnivores, and they have tentacles to capture prey
Platyhelminthes phylum
Domain Eukarya. Kingdom Animalia.
There are three types of acoelomate flatworms to know: planarians, flukes, and tapeworms. Planarians are free-living flatworms and are carnivores in marine or freshwater bodies of water. Flukes are internal/ external animal parasites that suck tissue fluids and blood. Tapeworms are internal parasites that often live in the digestive tract of vertebrates. Tapeworms appear segmented, but these segments, called proglottids, only develop secondarily for reproduction, and so tapeworms are not considered to be truly segmented animals. Tapeworms do not have a digestive tract, because they only need to absorb the predigested food around them. Other platyhelminths have a sac-like gut
Nematoda phylum
Domain Eukarya. Kingdom Animalia.
Otherwise known as roundworms and are pseudocoelomate with a complete digestive tract. Nematodes are free-living soil dwellers that help decompose and recycle nutrients. Trichnella spiralis is a type of nematode that causes trichinosis in humans when it is ingested via incompletely cooked meat. Nematodes can also be parasitic and are covered in a resilient substance called the cuticle which helps them resist degradation by the hosts. C. elegans is a type of nematode and used in research a lot.
Rotifera phylum
Domain Eukarya. Kingdom Animalia.
These are multicellular organisms with specialized organs enclosed in a pseudocoelom. They have a complete digestive tract and are filter- feeders. Rotifera are also capable of parthenogenesis, which is a type of asexual reproduction. In parthenogenesis, an unfertilized egg develops into an offspring. Because the unfertilized egg is haploid, there are mechanisms to restore the egg’s diploidy
Mollusca phylum
Domain Eukarya. Kingdom Animalia.
This group includes snails, octopus, squids, and bivalves. Octopus have highly developed nervous systems with complex brains. Bivalves have two- part shells and include organisms like clams and mussels. Most squids have small and internal shells, but octopus have no shells. Mollusks have coelomate bodies, complete digestive tracts, and usually have open circulatory systems with internal cavities called the hemocoel. The exoskeletons are composed of CaCO3. Mollusks can have amebocytes as well. There are a few classes of Mollusca to know:
i. Class Gastropoda
ii. Class Cephalopoda
iii. Class Bivalvia
Class Gastropoda
Domain Eukarya. Kingdom Animalia. Mollusca phylum.
The largest Molluscan class and includes animals such as slugs and snails. Gastropods are characterized by a single shell
Class Cephalopoda
Domain Eukarya. Kingdom Animalia. Mollusca phylum.
This class includes the octopus and squid. They have high O2 demand, giant nerve fibers, and closed circulatory systems
Class Bivalvia
Domain Eukarya. Kingdom Animalia. Mollusca phylum.
This class includes clams, mussels, scallops, and oysters
Annelida phylum
Domain Eukarya. Kingdom Animalia.
These are segmented worms which include leeches, earthworms, and polychaete worms. Leeches have suckers at both ends for attachment and movement. Leeches are predators of small animals and are blood parasites. Polychaete worms are mostly marine, but they exhibit a variety of lifestyles. Septa divide the coelom into separate compartments. Earthworms are very sensitive to salt, because it can destroy the sensitive skin of the earthworm that they require for respiration!
Arthropoda phylum
Domain Eukarya. Kingdom Animalia.
This groups includes spiders, insects, and crustaceans. Arthropods have jointed appendages which allows them to be successful. They also have well-developed nervous systems, specialized body segments, and exoskeletons made of chitin. Arthropods have two kinds of life cycles: nymphs or larvae. Nymphs are immature arthropods that look like small versions of the adults, and nymphs will undergo gradual metamorphosis as they grow. Larvae are maggots specialized for eating. Once they reach a certain size, the larvae will enclose themselves within a pupa (cocoon) to undergo metamorphosis into adults. These adult forms are specialized to disperse and reproduce. Arthropods make up the largest animal phylum. The classes you need to know include:
i. Class Insecta
ii. Class arachnida
iii. Class crustacea (subphylum)
Class Insecta
Domain Eukarya. Kingdom Animalia. Arthropoda phylum.
These organisms have three pairs of legs, one pair of antennae, and spiracles. Spiracles are tracheal tubes used for breathing. There are more insect species than any other class on earth
Class arachnida
Domain Eukarya. Kingdom Animalia. Arthropoda phylum.
These animals have four pair of legs and “book lungs,” which are respiratory structures that look like sheets of a book. Arachnids include spiders and scorpions. Arachnids do not have antennae
Class Crustacea (subphylum)
Domain Eukarya. Kingdom Animalia. Arthropoda phylum.
Crustaceans have segmented bodies and gills with a variable number of appendages. This class includes crabs, shrimps, lobsters, crayfish, and barnacles. Crustaceans have two pairs of antennae
Echinodermata phylum
Domain Eukarya. Kingdom Animalia.
This groups includes sea stars, urchins, and sand dollars. Echinoderms are coelomate and are deuterostomes. They have complete digestive tracts. The adults have radial symmetry, but they are bilateral when young. Because of their bilateral symmetry in youth, it is believed that their ancestors were bilateral. They lack segmentation
Chordata phylum
Domain Eukarya. Kingdom Animalia.
They have four main features, which sometimes may just be temporary and exist only during embryonic development.
i. Notochord
ii. Dorsal hollow nerve cord
iii. Pharyngeal gill slits
iv. Muscular tail
Notochord
Domain Eukarya. Kingdom Animalia. Chordata phylum feature
A dorsal, flexible rod
that functions as support. It is replaced by bone during development in most vertebrates. It becomes the nucleus pulposus within intervertebral discs. The notochord is derived from the mesoderm, and it defines the primitive axis of the embryo
Dorsal hollow nerve cord
Domain Eukarya. Kingdom Animalia. Chordata phylum feature
Forms the basis of the nervous system. In some chordates, the nerve cord becomes the brain and the spinal cord
Pharyngeal gill slits
Domain Eukarya. Kingdom Animalia. Chordata phylum feature
Provide channels across the pharynx to the outside body. The slits become gills for oxygen or for filter-feeding. However, the pharyngeal gill slits disappear during embryonic development in others. In fish, the gill pouch becomes fish gills. In mammals, the gill pouch becomes Eustachian tubes in the ears and other various head/neck structures
Muscular tail
Domain Eukarya. Kingdom Animalia. Chordata phylum feature
a.k.a. the post-anal tail. This tail is lost during embryonic development in humans and many other chordates
2 groups of chordates
Domain Eukarya. Kingdom Animalia. Chordata phylum
Invertebrates and vertebrate
Invertebrates include animals such as the lancelets and the tunicates. Vertebrates have vertebrae that enclose the spinal cord and include animals such as sharks, fish, amphibians, reptiles, birds, and mammals. Jawless fish (Agnatha) include the hagfish and lampreys. Lampreys are parasites, and hagfish are scavengers; jawless fish evolved before jawed fish. Reptiles have leathery eggs, thick skin, an amnion, and internal fertilization. Reptiles do not lose their gills at any stage of their development.
Archaeopteryx is the bird (disputed) link to dinosaurs and lived ~160 mya. Birds resemble reptiles today in that they lay eggs, have scaly legs, horny beaks, and contain reptilian internal structures.
Time periods
From the most recent to oldest time period: Cenozoic > Mesozoic > Paleozoic > Precambrian. A mnemonic for these time periods is Clean My Pale Pee. Dinosaurs appeared during the Mesozoic. The first land vertebrates, land plants, fish, and many algae appeared in the Paleozoic era. Invertebrates, monera, and fungi originated in the Precambrian (oldest) era.
Evolution order
The evolution order goes from: jawless fish, bony fish, amphibians, reptiles, birds, and lastly mammals. A mnemonic for this order is James Bond: A Real Barbaric Man
Seed
Includes the young dormant sporophyte, storage of nutritive tissue, and an outer protective coat. The seed has all the necessary info from its parental plants like a fertilized egg, and the seed just needs the proper environmental conditions to grow.
Cellular Division in plants
Alternation of generation is observed. There is an alternation of diploid (2n) and haploid (n) stages.
- Meiosis in sporangia produces haploid spores
- Spores undergo mitosis to become multicellular and become the gametophyte, which is still haploid (n) since the spores were already haploid
- The gametes fuse and produce a diploid cell (2n) that grows by mitosis to become a sporophyte
- Cells in the sporangia of the sporophyte undergo meiosis to produce haploid spores which germinate and repeat the life cycle
Vegetative propagation is a form of asexual reproduction in plants, leading to genetically identical offspring.
Angiosperm’s 2 groups
Dicotyledons (dicots) and monocotyledons (monocots).
Angiosperms are the most diverse type of plant and have dominated the land for over 100 million years.
Evolution order of plants starting from the oldest
Bryophytes, then gymnosperms, and then angiosperms
Cotyledons
Description: Storage tissue that provides nutrition to developing seedlings
Dicots: 2 cotyledons
Monocots: 1 cotyledon
Leaf venation
Description: Pattern of veins in leaves
Dicots: Netted, branching pattern
Monocots: Parallel
Flower parts
Description: Numbers of petals, sepals, stamens, and other parts
Dicots: In 4s, 5s, or multiples
Monocots: In 3s or multiples
Vascular bundles
Description: Arrangement of vascular tissues (xylem and phloem) in stems
Dicots: Organized in a circle
Monocots: Scattered
Root
Description: Form of root
Dicots: Taproot, which is a large single root
Monocots: Fibrous root system with many fine roots
Plant tissues
3 groups.
Ground tissues, dermal tissue, vascular tissue
Ground tissues
A type of plant tissue. These tissues provide structural support to the plant and thus make up most of the plant’s mass. There are three types of ground tissue
i. Parenchyma
ii. Collenchyma
iii. Sclerenchyma
Parenchyma
A type of ground tissue, which is a type of plant tissue.
This is the most common ground tissue. They have thin cell walls. Their function is storage, photosynthesis, and secretion. Mesophyll cells in leaves are examples of parenchyma tissue
Collenchyma
A type of ground tissue, which is a type of plant tissue.
They have thick but flexible cell walls, and serve mechanical support functions
Sclerenchyma
A type of ground tissue, which is a type of plant tissue.
They have thicker walls than collenchyma, and also provide mechanical support. Sclerenchyma tissue produces lignin, which is a strengthening polymer
Dermal tissue
A type of plant tissue.
This tissue includes epidermis cells that cover the outside of plant parts. Guard cells are a type of epidermal cells that surround stomata, hair cells, stinging cells, and glandular cells. In aerial portions of plants, the epidermal cells secrete a waxy protective substance that forms the cuticle. Roots do not have a cuticle covering since that would prevent the roots from absorbing water
Vascular tissue
A type of plant tissue.
This tissue consists of xylem and phloem which together forms vascular bundles.
i. Xylem
ii. Phloem
Xylem
A type of vascular tissue, which is a type of plant tissue.
This tissue conducts water
and minerals and also has functions in mechanical support. The xylem has a second cell wall for additional strength. In some places, the walls of xylem cells have pits because of the absence of the second cell wall. The cells are dead at maturity, meaning there are no cellular components – just cell walls. There are two kinds of xylem cells:
a. Tracheids
b. Vessel elements
Tracheids
A type of xylem cell, which is a type of vascular tissue, which is a type of plant tissue.
These structures are long and tapered where water passes laterally from one to another through pits
Vessel elements
A type of xylem cell, which is a type of vascular tissue, which is a type of plant tissue.
These structures are shorter and wider, and they have less or no taper at the ends. A column of vessel elements (members) is called a vessel. Perforations are where water passes through from one vessel member to the next. The members lack both first and secondary cell walls. Perforations are an advantage over the pits in tracheids because water moves more efficiently
Phloem
A type of vascular tissue, which is a type of plant tissue.
This tissue transports sugar. It is made of cells called sieve-tube members (elements) that form fluid conducting columns called sieve tubes. The cells are alive at maturity but lack nuclei and ribosomes. Pores on the ends of members form sieve plates, which are areas where the cytoplasm of one cell makes contact with the next cell. Sieve tubes are associated with companion cells, which are living parenchyma cells that lie adjacent to each sieve-tube member. Sieve tubes are connected by plasmodesmata to maintain physiological support due to the lack of nuclei in the sieve-tube members
The seed
Consists of the embryo, the seed coat, and some kind of storage material in the form of endosperm. In many monocots, the endosperm is the primary storage tissue, and cotyledons function to transfer nutrients from the endosperm to the embryo. The embryo consists of multiple parts:
- epicotyl
- plumule
- hypocotyl
- radicles
- coleoptiles
Epicotyl
Part of the embryo of seed.
This part is at the top portion of the embryo and becomes the shoot tip
Plumule
Part of the embryo of seed.
These are young leaves often attached to the epicotyl and located underneath the epicotyl. The plumule can refer to both together
Hypocotyl
Part of the embryo of seed.
This part is located at the bottom region of the young shoot. It is located below the plumule and attached to cotyledons
Radicles
Part of the embryo of seed.
Develop from below the hypocotyls and become the roots
Coleoptiles
Part of the embryo of seed.
This is a sheath in monocots that surrounds and protects the epicotyl. In developing young plants, coleoptiles appears first, and then the true leaves from the plumule break through the coleoptile
Germination and development
The seed remains dormant at maturity until specific environmental cues such as water, temperature, light, or seed coat damage breaks the seed’s dormancy period. Some seeds may have required dormancy periods where germination will not happen regardless of environmental cues.
Germination begins with imbibition (absorption) of water. Enzymes are then activated to start biochemical processes, and respiration begins. The absorbed water causes the seed to swell and for the seed coat to crack. The growing tips of the radicle produce roots that anchor the seedling. The hypocotyl elongates and the young shoot is formed.
In young seedlings/plants, growth occurs at the tips of roots and shoots. These tips are called apical meristems. Meristematic cells are areas of actively dividing, mitotic cells, and this causes growth. Growth at the apical meristems is called primary growth, and it produces primary tissues - primary xylem and primary phloem elongation. Apical growth also causes vertical growth. Most plants, including most monocots, just have this type of growth. Lateral meristems can be found on the sides of plants which causes growth in thickness and width.
Root growth sections
Root cap, Zone of cell division, Zone of elongation, Zone of maturation
The description for root growth is very similar for shoot tip growth, except there is no root cap present in shoot tip growth
Root cap
A root growth section.
a.k.a. root tip, it protects the apical meristem behind it. The root cap secretes polysaccharides that moisten the soil, permitting root growth
Zone of cell division
A root growth section.
This zone is formed from the dividing cells of the apical meristem. This zone is right above the apical meristem
Zone of elongation
A root growth section.
Newly formed cells from the zone of cell division absorb water and elongate. This zone is responsible for our perception of growth
Zone of maturation
A root growth section.
The cells differentiate and mature into the xylem, phloem, parenchyma, or epidermal cells (root hairs may grow here)
Primary Growth Vs. Secondary Growth
Conifers and woody dicots undergo secondary growth in addition to primary growth. Secondary growth increases girth, and is the origin of woody plant tissues. Secondary growth occurs at the two lateral meristems: the vascular cambium (secondary xylem and secondary phloem) and the cork cambium (gives rise to periderm-protective material that lines the outside of woody plants).
Primary Structure of Roots
From the outside of the root structure to the center: epidermis, cortex, endodermis, vascular cylinder (stele)
Root hairs function in mineral exchange with the soil.
Note that rhizomes are underground stems that can sprout to produce new shoots and roots for the plant.
Epidermis
Part of primary structure of roots.
The epidermis lines the outside surface of the root. In the zone of maturation, the epidermal cells produce root hairs. When the zone of maturation ages, the root hairs die. New epidermal cells from the zone of elongation becomes the cells of the new zone of maturation, and then forms the new root hairs to continue the absorption of water. The old epidermis functions to protect the root
Cortex
Part of primary structure of roots.
This makes up the bulk of the root. The cortex stores starch and contains intercellular spaces to provide aeration of cells for respiration
Endodermis
Part of primary structure of roots.
This is a ring of tightly packed cells at the inner-most portion of the cortex. A band of fatty material (suberin) impregnates endodermal cell walls to form an encircling band called the Casparian strip. The Casparian strip creates a water-impenetrable barrier between cells. All water passing through the endodermis must pass through the cytoplasm of endodermal cells and not through the cell walls, because the cell wall has no means of filtering substances. The Casparian strip forces the movement of water into the center of the root and prevents water from moving back out to the cortex
Vascular cylinder (Stele)
Part of primary structure of roots.
The stele is made up of vascular tissue (phloem and xylem) and the pericycle. The stele is located within the endodermis. The outer part of the stele consists of one or several layers of cells called pericycle, from which lateral roots arise. Inside the pericycle is vascular tissues
• Dicot - the xylem cells fill the center of the vascular cylinder, and phloem is arranged to form an X shape
• Monocot - groups of xylem and phloem alternate in a ring with the pith in the middle
Primary Structure of Stems
Stems lack an endodermis and Casparian strips. Stems include these structural components:
Epidermis, cortex, vascular cylinder
Epidermis
Part of primary structure of stems.
The epidermis contains epidermal cells covered with a waxy (fatty) cutin, which forms a protective layer called the cuticle
Cortex
Part of primary structure of stems.
This is ground tissue that lies between the epidermis and the vascular cylinder. The cortex can contain chloroplasts
Vascular cylinder
Part of primary structure of stems.
The cylinder consists of xylem, phloem, and pith. In dicots and conifers, the xylem and phloem are grouped in bundles with the xylem on the inside and the phloem on the outside. The bundles form a ring around the central pith area. A single layer of cells between the xylem and the phloem may remain undifferentiated and later become the vascular cambium
Secondary Structure and Secondary Growth of Stems and Roots
The vascular cambium is located between the primary xylem (located closer to the center) and the primary phloem (located closer to the outside). The vascular cambium is a cylinder of tissue that extends the length of the stem and the root. The vascular cambium is meristematic and causes secondary growth. There are 4 steps of secondary growth.
Wood is formed from mature (dead) xylem tissues. Only the more recent secondary xylem produced from the vascular cambium remains active to transport water, also termed as sapwood. Older xylem located at the center functions only as support. This older xylem is also known as heartwood, which is also dead wood.
Annual rings are created from the continuous growth of secondary xylem. The size of the rings indicates the rainfall history, while the number of rings indicates the age of the tree.
Step 1/4 of secondary growth of stems and roots
Cells in the vascular cambium divide. The cells on the inside of the vascular cambium become the secondary xylem, while cells on the outside of the vascular cambium become the secondary phloem
Step 2/4 of secondary growth of stems and roots
Over the years as the vascular cambium continues to divide, the secondary xylem accumulates and increases the girth of the stem and root. Secondary xylem is continuously added over the years
Step 3/4 of secondary growth of stems and roots
On the edge of the vascular cambium layer, new secondary phloem is added yearly which replaces the previous secondary phloem, unlike secondary xylem. As a result, tissues beyond the secondary phloem are pushed outward as the xylem increases its girth. The primary tissues (epidermis and cortex) thus break apart and are shed
Step 4/4 of secondary growth of stems and roots
In order to replace the shed epidermis, the cork cambium (located beyond the phloem and closer to the edge) produces new cells on the outside which becomes cork, which is impregnated with suberin. Cells can grow towards the center of the plant from the cork cambium, which is then called the phelloderm. Together, the cork, cork cambium, and phelloderm are called the periderm. In the stems of dicots and conifers, the cork cambium originates from the cortex just inside the epidermis. In roots, it originates from the pericycle
Structures of The Leaf
Epidermis, Palisade mesophyll, spongy mesophyll, Guard cells, Vascular bundles
Epidermis
Structure of the leaf.
This is a protective layer(s) that is covered with a cuticle (protective layer containing waxy cutin) which reduces transpiration. Transpiration is water loss through evaporation. The epidermis may bear trichomes. Examples of trichomes include hair, scales, glands, outgrowths, etc.
Palisade mesophyll
Structure of the leaf.
This layer consists of parenchyma cells with chloroplasts and large surface areas. The palisade mesophyll is specialized for photosynthesis. The palisade mesophyll is oriented and packed at the upper surface of the leaf, but plants in dry habitats can have palisade mesophyll layers on both surfaces. The primary area for leaf photosynthesis occurs at this layer
Spongy mesophyll
Structure of the leaf.
This layer has parenchyma cells loosely arranged below the palisade mesophyll. Numerous intercellular spaces provide air chambers for carbon dioxide to reach photosynthesizing cells, and for oxygen to reach respiring cells
Guard cells
Structure of the leaf.
These are specialized epidermal cells that control the opening and closing of stomata. Therefore, guard cells also control gas exchange
Vascular bundles
Structure of the leaf.
These bundles
consist of xylem (water for photosynthesis) and phloem (transports sugar and by-products of photosynthesis to other parts of the plant). Bundle sheath cells surround the vascular bundle, so no vascular tissue is exposed to intercellular space. This also prevents air bubbles from entering which otherwise would impede the movement of water. Vascular bundles also provide an anaerobic environment for carbon dioxide fixation in C4 plants
Transport of water
Water enters the root through root hairs by osmosis. There are two pathways for water to move through roots: Apoplastic pathway and symplastic pathway.
Once the water reaches the endodermis, it can only enter into the stele (vascular cylinder) by the symplastic pathway due to Casparian strips blocking the movement of water through cell walls. and is selective permeable (K+ pass, Na+ is blocked - common in soil but unused in plants) confused on this. Once the water moves through the endodermis, the apoplastic pathway takes over to reach the xylem (which is the major conduction pathway via tracheids and vessels).
Water moves up through the plant in several ways: osmosis, capillary action, cohesion-tension theory
Apoplastic pathway
A pathways for water to move through roots.
Water moves through cell walls and intercellular spaces from one cell to another without ever entering the cells
Symplastic pathway
A pathways for water to move through roots.
Water moves through the cytoplasm of one cell to another through plasmodesmata (small tubes that connect cytoplasm of adjacent cells)
Osmosis
A method for water to move up through the plant.
Water moves from the soil through the root and into the xylem by a concentration gradient. Water is continuously moved out of the root and into the xylem, leaving behind a higher mineral concentration inside the stele. This then drives more water to enter the roots. This osmotic force (root pressure) can be seen as guttation, which is the formation of small droplets of sap (water and minerals) on the ends of leaves in the morning. But mostly, root pressure is too small to have a major effect on water transport
Capillary action
A method for water to move up through the plant.
Causes the rise of liquids in narrow tubes, and it can also contribute to the movement of water up the xylem. Capillary action results from forces of adhesion (molecular attraction between unlike substances) between water and the xylem. A meniscus is formed at the top of the water column. No meniscus forms in an active xylem since water forms a continuous column. The capillary effect is minimal
Cohesion-tension theory
A method for water to move up through the plant.
Most water movement is explained by this theory, and thus is the major contributor of water movement. This theory consists of: transpiration, cohesion and bulk flow
Transpiration
Part of the cohesion-tension theory.
This is what causes the evaporation of water from plants. Transpiration is when water evaporates from leaves, which causes negative pressure (tension) to develop within leaves and the xylem
Cohesion
Part of the cohesion-tension theory.
This is the attraction between like substances, such as the attraction between many water molecules. Cohesion allows water within xylem cells to behave as a single, polymer-like column from the roots to the leaves
Bulk flow
Part of the cohesion-tension theory.
When a water molecule is lost from a leaf by transpiration, it pulls up behind it an entire column of water molecules. Bulk flow is generated by transpiration, which is itself caused by the heat action of the sun, so technically the sun drives sap ascent
Control of Stomata
Open vs. closed stomata affects gas exchange, transpiration, sap ascent, and photosynthesis. When stomata are closed, CO2 is not available, and the plant cannot photosynthesize. When stomata are open, CO2 can enter the leaf for photosynthesis, but the plant risks desiccation from transpiration.
Guard cells
Exist in pairs and surround the stomata. The cell walls of guard cells do not have the same thickness all around (the cell wall is thicker when it borders the stomata). Guard cells expand when water diffuses in. Due to the irregular thickness and radial shape of the cell, the sides with thinner cell walls expand more to create an opening (stoma). When water diffuses out, the kidney shape collapses and the stoma closes.
Factors involved in the mechanism of opening and closing the stoma
- High temperatures will cause the stoma to close
- If there is low CO2 inside the plant, the stoma will open to allow for photosynthesis
- Stoma can close at night and open during the day. CO2 is low during daylight because it is used during photosynthesis. At night, there are high levels of CO2 because of respiration. Stoma can open during the day to intake more CO2 to continue with photosynthesis. Stoma can close at night because the plant does not need more CO2 for photosynthesis
Stomata opening and potassium
Stomata opening is caused by the diffusion of potassium ions into guard cells. This creates a gradient that causes more water to move in. When potassium ions enter the cell, that creates an unbalanced charge state. Chloride ions can also enter the guard cells to balance out the additional positive charges from the potassium ions, or protons (from the ionization of the cell’s organic substances) can get pumped out.
Guard cells and blue light
Guard cells also have a blue light receptor on their plasma membranes. When stimulated with blue light, the stomata opens.
Transport of Sugars
Translocation is the movement of carbohydrates through the phloem from a source (e.g. leaves) to sink (the site of carbohydrate utilization). This movement is described by the pressure-flow hypothesis:
- Sugars enter the sieve-tube members
- Water enters sieve-tube members
- Pressure in the sieve-tube members at the source moves water and sugars to sieve-tube members at the sink through sieve tubes
- Pressure is reduced in sieve-tube members at the sink as sugar is removed for utilization by nearby cells
Sugars enter the sieve-tube members
Step 1/4 of pressure-flow hypothesis.
Soluble carbohydrates move from the site of production (palisade mesophyll) to phloem sieve-tube members by active transport. There is a higher solute concentration at the source than at the sink (roots)
Water enters sieve-tube members
Step 2/4 of pressure-flow hypothesis.
Water diffuses into the source by osmosis to balance the lower water concentration from the previous step
Pressure in the sieve-tube members at the source moves water and sugars to sieve-tube members at the sink through sieve tubes
Step 3/4 of pressure-flow hypothesis.
When water enters the sieve-tube members, pressure builds up since the rigid cell walls do not expand. As a result, the water and sugar move by bulk flow through the sieve tubes (through plates between sieve-tube members)
Pressure is reduced in sieve-tube members at the sink as sugar is removed for utilization by nearby cells
Step 4/4 of pressure-flow hypothesis.
Pressure begins to build up at the sink (from bulk flow from source to sink). However, the sink is where sugars are used. The sugars are removed from sieve-tube members by active transport. This increases the water concentration at the sink. Water then diffuses out of the cell and relieves pressure. Cells store energy as insoluble starch. The benefit of this is that any cell can act as a sink and get the sugar and water transported there. Likewise, by breaking down starch, any cell can act as a source (e.g. plant roots at night break down starch when photosynthesis activity is low, and they act as a sugar source).
Auxin (IAA-indoleacetic acid)
A plant hormone.
Promotes plant growth and elongation of cells by increasing the proton concentration in primary cell walls. Enzymes are activated that loosen cellulose fibers which increases cell wall plasticity, and thus the turgor pressure expands cells to grow. This hormone is produced at the tips of shoots and roots (apical meristem). In concert with other hormones, auxin influences a plant’s response to light (phototropism) and gravity (geotropism). Auxin is a modified tryptophan amino acid. After synthesis, the hormone is actively transported (ATP) from cell to cell in a specific direction (polar transport) by means of chemiosmotic process. Auxin inhibits lateral buds when it is produced at the terminal buds of a growing tip. It moves unidirectionally from shoot to root
Gibberellins (GA)
A plant hormone.
A group of hormones that promotes cell growth (flower and stem elongation). Gibberellins are synthesized in young leaves/roots/seeds and then transported to other parts of the plant. Gibberellins can act together with auxins to stimulate growth. GA are involved in the inhibition of aging in leaves, promotion of fruit development, and seed germination. Gibberellin is released from the embryo, and it moves through the endosperm to the aleurone layer. Aleurone then secretes digestive enzymes (amylase) to break down the endosperm starch into sugars for nourishment, and then germination commences. A high concentration of gibberellins causes bolting, which is the rapid elongation of stems
Cytokinins
A plant hormone.
Stimulates cytokinesis, and it also stimulates and influences the direction of organogenesis. Cytokinins stimulate the growth of lateral buds, which weakens the apical dominance created by auxins. Apical dominance is when the growth of the apical meristem is dominant. Cytokinins also delay senescence (aging) of leaves. The effects of cytokinins depend on the target organ and the presence/concentration of auxin. Structurally, cytokinins have variations of the nitrogen base adenine. Cytokinins include the naturally occurring zeratin and the artificially produced kinetin
Ethylene (H2C=CH2)
A plant hormone.
A gas that promotes the ripening of fruit, the production of flowers, and influences leaf abscission and apoptosis. Abscission is the shedding of certain parts of an organism. Specifically for plants, the most well known abscission is the loss of leaves each year. Together with auxin, ethylene can inhibit elongation of roots, stems, and leaves. Ethylene stimulates ripening by the enzymatic breakdown of cell walls. Because of ethylene, ripe fruit in proximity to a spoiled one will also get spoiled since ethylene is gaseous. Ethylene causes the triple response in plants so they can grow around objects if necessary
Abscisic acid (ABA)
A plant hormone.
Growth inhibitor. In buds, it delays growth and forms scales, and maintains dormancy in seeds. Dormancy can be broken by an increase in gibberellins or by mechanistic responses to environmental cues such as temperature and light
Plant Responses to Stimuli
Since plants are anchored by their roots, they cannot move to respond to environmental stimuli. Instead, plants can change their growth pattern due to environmental stimuli. Tropism is a growth pattern in response to an environmental stimulus in plants and auxins. There are several types of tropisms in plants:
- Phototropism
- Gravitropism (geotropism)
- Thigmotropism
Phototropism
A type of tropism in plants.
This is when a plant grows towards a light source. Auxin produced in the apical meristem moves downward by active transport into the zone of elongation, which generates growth by stimulating elongation. The plant stem grows straight when all sides of the apical meristem are equally illuminated. But, plant growth can be differential if the plant is not equally illuminated. If this happens, auxins move more towards the shady side, and thus the stem bends and grows more towards the light
Gravitropism (geotropism)
A type of tropism in plants.
This is a plant’s response to gravity by the stems and roots. Auxin and gibberellins are involved. If the stem is horizontal, auxin concentrates on the lower side and the stem bends upward. If the root is horizontal, auxin produced at the apical meristem moves up in the roots and concentrates on the lower side. However, auxin inhibits growth in roots due to the higher auxin concentration at roots than stems. Thus, the lower side grows less, and the roots curl down. Note however, that dissolved ions, auxins, gibberellins, and other hormones do not directly respond to gravity. But, starch is insoluble in water and does respond to gravity. It is believed that specialized starch-storing plastids called statoliths, which settle at the lower ends of cells, somehow influence the direction of auxin movement
Thigmotropism
A type of tropism in plants.
This is a plant’s response to touch. For example, thigmotropism can be seen when vines wrap around an object that they are in contact with
Photoperiodism
Photoperiodism is a response in plants to changes in photoperiod. Photoperiod is the daily illumination that an organism receives. Plants maintain a circadian rhythm, which is an internal clock that measures the length of daylight and night. The circadian rhythm is an endogenous mechanism, meaning the the clock continues to keep track of time even if external cues are absent. External cues such as dawn and dusk, however, can reset the clock for accuracy.
Phytochromes
In order for plants to exhibit photoperiodism, they need phytochromes. Phytochromes are proteins modified with light-absorbing chromophores. There are two forms of phytochromes: Pr (P660-red) and Pfr (P730-far red). These two forms of phytochromes are reversible. When Pr absorbs red light, it gets immediately converted to Pfr. When Pfr absorbs far-red light, it is immediately converted back to Pr. Pfr is the phytochrome’s active form. Pfr appears to reset the circadian rhythm clock to maintain accuracy. Pr is the form of phytochrome synthesized in plant cells, specifically in leaves.
Pr and Pfr
Pr and Pfr are in equilibrium during daylight because sunlight exhibits both red light and far- red light. Pr then accumulates at night since the cells keep making Pr at night, but there is no sunlight to convert Pr to Pfr. Pfr breaks down faster than Pr and is also converted back to Pr metabolically, thus Pr accumulates. At daybreak, light rapidly converts the accumulated Pr to Pfr, and then equilibrium is maintained.
Night length, flashes of red
The night length is responsible for resetting the clock. If daylight is interrupted with a brief dark period, there is no effect. However, flashes of red and far-red during the night period can reset the clock. Only the last flash affects the night length. Red flashes result in shorter night lengths, and far-red flashes restore the night length.
- Flash of red during the night: Pr is converted to Pfr, a shorter night period is measured, and the circadian rhythm resets
- Flash of far-red after a red flash will reverse the effect of the red light, and the night length will be restored to before
- In a series of alternating flashes, only the last one affects the perception of night length: red flashes shorten the night length, while far-red flashes restore the night length
Flowering plants initiate flowering in response to changes in photoperiod.
- Long-day plants - these plants flower in the spring and early summer when daylight is increasing
- Short-day plants - these plants flower in late summer and early fall when daylight is decreasing
- Day-neutral plants - these plants do not flower in response to daylight changes but due to temperature or water instead
When flowering is initiated, the florigen hormone is produced in leaves and travels to shoot tips.
Phytochrome is involved in other light-related functions: (1/4)
- Many seeds require minimum light exposure before germinating. Red light stimulates seed germination. The phytochrome system detects changes in the amount of light. If that minimum amount of light exposure is exceeded, or due to other facts like the presence of water, giberellins will be produced (or ABA destroyed) and the seed will germinate
Phytochrome is involved in other light-related functions: (2/4)
- Red to far-red ratio is measured by phytochromes to sense the quality of light. For example, phytochromes can sense if a plant is being shaded by other plants. If a shade-intolerant plant is shaded, it can stimulate growth
Phytochrome is involved in other light-related functions: (3/4)
- In C3 plants, CO2 levels are relatively low in leaves when photosynthesis is active during the day and when stomata are open. At night, stomata close and CO2 levels in leaves increase due to respiration
Phytochrome is involved in other light-related functions: (4/4)
- In CAM plants, stomata are closed during the day but photosynthesis proceeds because of CO2 supplied by the metabolic conversion of malic acid
Chemoautotrophs
use energy from chemical reactions and carbon from inorganic compounds to make food
Photoautotrophs
use light energy and carbon from inorganic compounds to make food
Chemoheterotrophs
use energy from chemical reactions and carbon from organic compounds to make food
Photoheterotrophs
use light energy and carbon from organic compounds to make food
Heterotrophs
Carbon obtained by metabolizing organic compounds
Autotrophs
Carbon obtained by fixing carbon dioxide
Organotrophs
Electrons obtained from organic compounds. Electrons needed for redox reactions during ATP synthesis and biosynthesis of other compounds
Lithotrophs
Electrons obtained from inorganic compounds such as sulfur, nitrogen, carbon and iron containing compounds
Flagella composition in prokaryotes vs eukaryotes
Flagella made of flagellin in prokaryotes, but tubulin in eukaryotes
Are roundworms segmented?
No, but earthworms are
Acoelomate phyla
porifera, cnidaria, platyhelminthes
i.e. tapeworm in platyhelminthes
Pseudocoelom phyla
Nematoda, rotifera
i.e. roundworm in nematoda
Coelomate phyla
Mollusca, annelida, arthropoda, echinodermata, chordata
Countercurrent exchange
In gas exchange in fish gills, temperature regulation in animals and concentration gradient in loop of Henle
