Table of Contents
As defined by botany, any eukaryotic species of the biological kingdom Plantae that is photosynthetic and has a rigid cell wall. Planta is a Latin word that means “sprout, shoot, cutting.”
A plant is any eukaryotic organism that belongs to the Plantae biological kingdom. In the strictest sense, plants are embryophytes, that included vascular plants, liverworts, hornworts, and mosses. In certain less stringent references, green algae was considered a plant in certain less stringent references. Green algae include both unicellular and multicellular species with chloroplasts and cell walls.
Autotrophs are plants that eat just their own kind of food. Photosynthesis is how they produce their own nourishment. They can capture energy through the chloroplast’s green pigment (chlorophyll) and use carbon dioxide and water to create carbohydrates as food and oxygen as a by-product.
Plants are typically found at the top of the food chain since they are autotrophs. They’re referred to as “producers.” Other creatures, especially mammals, consume them as food. Animals, on the other hand, are heterotrophs, meaning they must devour other species to survive.
Some animals (especially herbivores) consume just plants, whereas others eat only meat or a combination of animal and plant matter. Plants do not rely on animals to develop and thrive since they are capable of producing their own nourishment.
A group of carnivorous plants (such as the Venus flytrap) that catch and devour animal prey, primarily when photosynthesis is difficult, is an exception.
Plants are eukaryotes, or multicellular organisms. Plants, like mammals, have a membrane-bound nucleus inside their cells. The nucleus is an organelle that houses genes on chromosomes. Golgi apparatus, endoplasmic reticulum, lysosomes, peroxisomes, and plastids are further organelles suspended in the cytoplasm of a plant cell.
Plastids are found in plants. Plastids inside a eukaryotic cell indicate that it is more likely a plant than an animal. Plastids are available in a wide range of forms and sizes.
Chloroplasts are photosynthesis-related plastids that contain chlorophyll (green pigments). Apart from green, chromoplasts include pigments and are involved in pigment production and storage. Light energy is absorbed by chlorophyll systems at certain wavelengths in the electromagnetic spectrum.
Pigments also contribute to the colour of plant structures (e.g. green leaves, red flowers, yellow fruits). Non-pigmented plastids, such as amyloplasts, elaioplasts, and proteinoplasts, are known as leucoplasts. Their primary use is to store food. Sugar, such as starch, is used by plants to store food.
Inside the cell of plants, there is a huge vacuole. This cytoplasmic structure is important in turgor pressure control.
Apart from the plasma membrane, plants have stiff cell walls. A plant cell’s cell wall provides additional structural support.
Plants do not have a skeletal structure like animals, but their cell walls are largely made of cellulose material, which helps to provide structural support.
Plants have a unique cell division system in which daughter cells are separated by a cell plate (phragmoplast). Plants do not have the same mobility as mammals. They are unable to go from one area to another at their leisure. As a result, they must contend with extreme weather, such as heat. Their cell walls, which keep their bodies from drying up, are one of the ways they can endure heat.
Plants, meanwhile, continue to move, albeit in a different way. The folding of the leaflets of the plant Mimosa pudica when touched, for example, and the shutting of the leaf of the Venus flytrap while trapping prey are both examples of nastic movement.
Some plants, such as the silver birch Betula pendula, would even droop their branches and leaves at night, as if they were “sleeping.” Tropism is another type of plant movement.
Tropism, on the other hand, is more of a response to a stimulus than a movement. Plants, for example, prefer to grow towards the light source (phototropism).
Plasmodesmata are plasmodesmata found on plants. Plants contain plasmodesmata, which behave as if they were cell connections between plant cells, but animals have cell junctions that keep cells in an animal tissue.
These cytoplasmic bridges between neighbouring cells are formed by the cell wall. These “bridges” assist maintain the tonicity of plant cells by facilitating cell contact and allowing fluid circulation.
Plants are multicellular, with numerous cells organised into tissues and organs that work together to accomplish a specific purpose.
Anchorage, support, and photosynthesis are all specific functions of plant organs (e.g. roots, stems, leaves, etc.) Plants can grow indefinitely thanks to their meristematic tissues. Indeterminate, actively dividing cells make up the tissue, which gives birth to differentiated tissues including epidermis, trichomes, phellem, and vascular tissues.
Plants do not have sensory organs, yet they may detect their surroundings in a variety of ways. Despite their absence of eyes, ears, and noses, plants can “see,” “hear,” and “smell.” They appear to “feel” and respond in ways that animals do not.
Plants may not have the same nervous system as mammals, but they appear to have their own system based on how they respond to their environment.
Despite not having eyes, Arabidopsis has photoreceptors (at least 11 kinds) that let the plant perceive light. Herbivory, for instance, might cause the release of specific compounds on the damaged plant component.
Herbivores are deterred by the production of defensive compounds by plants. Tomatoes have been seen emitting volatile signals to warn adjacent plants of an imminent herbivore assault.
Plants reproduce in two ways: asexually and sexually. Plants reproduce asexually by budding, fragmentation, fission, spore development, vegetative propagation, apomixis, and other methods.
Male and female gametes merge during fertilisation, resulting in sexual reproduction. In general, the plant life cycle includes generational alternation, or the sporophyte and gametophyte stages alternating.
Plants are able to “breathe.” Carbon dioxide from the atmosphere enters the plant cell through stomata. Carbon dioxide is transformed to oxygen during photosynthesis, which the plant releases as a metabolic by-product into the environment through the stomata.
Plants may lack other biological systems, but they do generate compounds that aid in plant defence and immunological activities, as well as plant hormones that operate as signalling molecules.
Plant Body Embryophytes have two primary organ systems: one for the shoots and another for the roots. The shoot system comprises of body components in the plant’s top section, whereas the root system consists of body parts in the bottom region.
Plant parts such as stems, branches, leaves, flowers, and fruits may all be found in the shoot system. They are frequently seen above ground. Roots, tubers, and rhizomes are all part of the root system. They are frequently discovered underground.
Plant tissues include the following:
1. Plant tissues made up of undifferentiated and mitotically active cells are known as embryonic or meristematic tissues. Apical meristem and cambium are two examples.
2. Permanent tissues are differentiated cell-based plant tissues. Fundamental (e.g., parenchyma, collenchyma, sclerenchyma) and complex (e.g., parenchyma, collenchyma, sclerenchyma) permanent tissues can be further divided (e.g. phloem and xylem tissues)
3. Reproductive tissues are those parts of the plant that are engaged in reproduction. The sporogenous tissues are one example.
Plant cells are eukaryotic, meaning they have a well-defined nucleus. The chromosomes that carry genes are found in the nucleus. The endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, and plastids are the other organelles except the nucleus.
Chloroplasts (containing chlorophyll, a green pigment), chromoplasts (with colours other than green), and leucoplasts (with pigments other than green) are the three types of plastids (colorless plastids). The vacuole is a huge structure inside the plant cell. It’s in charge of keeping turgor pressure in check.
The cytoplasm, where these organelles are suspended, is surrounded by the plasma membrane. The cell has a second layer, the cell wall, in addition to the plasma membrane. The cell wall, on the other hand, is not unique to embryophytes. Other species with cell walls include fungus, algae, and certain bacteria.
Primary and secondary cell walls make up the cell walls of embryophytes. Cellulose, hemicelluloses, and pectin make up a main cell wall. A thicker layer is the secondary cell wall. It contains a lot of lignin, which helps to reinforce and waterproof the wall.
One of the numerous functions of the cell wall is to aid in the resistance to osmotic pressure. Water flows into a plant cell when it is put in a hypertonic solution, causing the cell to expand. During severe osmosis, the existence of the cell wall prevents the cell from bursting.
Water diffuses out of a plant cell when it is put in a hypotonic solution, and turgor pressure is reduced, causing the cell to become flaccid. Further water loss will cause plasmolysis, which will eventually lead to cytorrhysis, or the total collapse of the cell wall.
Photosynthesis, respiration, transpiration, tropisms, nastic movements, photoperiodism, circadian rhythms, seed germination, and dormancy are all essential physiological activities that plants do.
Plants’ genomes are rather big. With roughly 94,000 genes, the wheat Triticum asestivum genome is the biggest of the plant genomes that have been sequenced.
Plant Life Cycle
Plants have two generations in their life cycle: gametophyte generation and sporophyte generation. Alternation of generations refers to the transition between diploid and haploid forms. Certain algae, such as Archaeplastida and Heterokontophyta, have this behaviour.
The sporophyte and the gametophyte are separate organisms in algae with generations that alternate. The gametophyte generation in embryophytes is one in which the phase begins with a haploid spore (n). To become a gametophyte, the spore goes through a sequence of mitotic divisions.
A haploid multicellular plant type is known as a gametophyte. There would just be one pair of chromosomes. Because the gametophyte phase is the sexual phase of the life cycle, the plant will grow sex organs that generate haploid gametes. Following the union of gametes, the gametes that participated in fertilisation would join the sporophyte generation, which is characterised by a diploid plant form.
The sporophyte is the main phase of tracheophytes (vascular plants) and is multicellular. As a result, the sporophyte is the most visible plant. The gametophyte, on the other hand, is the dominant plant in bryophytes (mosses and liverworts), and hence the predominant plant we see.
Tracheophytes’ life phases begin with a seed, which develops into a scion when conditions are favourable for development. The scion develops leaves, stalks, and branches as it grows. It grows into an adult plant that produces blooms in the end.
Sex cells are found in the flowers, such as sperm cells in pollen grains and ova in the ovary’s ovules. The seed contains a zygote formed by the fusion of the sex cells. Plants that are monoecious have both sex cells, whereas dioecious plants only have one kind of sex cell.
Plants can reproduce asexually as well. They achieve this by avoiding the use of gametes. Budding, fragmentation, fission, spore generation, vegetative propagation, and apomixis are all examples of asexual reproduction.
The ageing process of plants is referred to as plant senescence. During leaf senescence, for example, the yellowing of leaves happens as a result of chlorophyll breakdown, leaving only the carotenoids. However, certain plants, such as deciduous trees, may continue to produce new leaves.
Plants do not need to hunt or eat animals for nourishment since they are capable of photosynthesis (with the exception of carnivorous plants). They can create their own food by combining light energy, atmospheric carbon dioxide, and water molecules.
Nonetheless, the waste that animals exhale during breathing is one source of carbon dioxide. They give out oxygen as a waste product of photosynthesis in exchange. Animals, like other aerobic creatures, require oxygen to survive.
Other essential nutrients are obtained by plants from dissolved minerals in the soil. They take them in via their roots.
Calcium, magnesium, nitrogen, phosphorus, potassium, and sulphur are some of the macronutrients they get from the soil. Plants absorb boron, chloride, copper, iron, manganese, and molybdenum as micronutrients.
As a result, the breakdown of dead plant parts, or the entire plant, results in the return of important minerals and chemicals to the Earth.
They are frequently put at the top of a food chain due to their feeling of independence. In an ecosystem, they are the primary producers. As a result, plant extinction can have a significant influence on an ecosystem.
The Red List of Threatened Species of the International Union for Conservation of Nature (IUCN), a system for monitoring the conservation status of species across the globe, used a method of categorising species based on extinction risk. As a result, species can be classified as “data deficient,” “near-threatened,” “vulnerable,” “endangered,” “critically endangered,” “regionally extinct,” “extinct in the wild,” and “extinct.”
In 2016, the International Union for Conservation of Nature (IUCN) listed 2,493 plants as critically endangered and 3,654 species as endangered.
Plants develop symbiotic relationships with other species. Here are several examples:
1. Mutualism – for example, plants provide nectar for honeybees, while honeybees aid in the dispersion of pollen grains.
2. Predation – for example, carnivorous plants that eat insects and other tiny animals
3. Competition – for example, plants that compete for available space and nutrients with other plants for habitat.
4. Commensalism – for example, plant fruits that adhere to animal hair for free transportation.
5. Parasitism – for example, parasitic plants that obtain nutrients from their hosts, such as Cuscuta (dodder), which attaches to an acacia tree and develops haustoria that absorb nutrients.
The Census of Marine Life projected in 2011 that there might be about 8.7 million eukaryote species on Earth, including about 298,000 plant species. There have previously been 215, 644 described and catalogued.
Organelles such as plastids and mitochondria, according to the endosymbiotic hypothesis, reflect once free-living prokaryotes. The chloroplasts appear to be connected to cyanobacteria, which are prokaryotic microorganisms.
The structural similarity between cyanobacteria and chloroplasts provides the foundation. Furthermore, they share the same photosynthetic pigments as the genome and a single circular DNA molecule.
Endosymbiotic processes, it appears, were responsible for the emergence of the earliest photosynthetic eukaryotes one billion years ago. The embryophytes are thought to have evolved from Charophyta (a kind of green algae).
Many similarities exist between charophytes and embryophytes, such as the development of phragmoplasts during mitosis.
The following is a short chronology of embryophyte evolution:
Phanerozoic aeon » Paleozoic era » Ordovician period: The first embyophytes (land plants) arose during the Ordovician epoch (485 million years ago to 440 million years ago).
Phanerozoic eon » Paleozoic era » Devonian period: Primitive plants, trees, and shrub-like forests dominated the earth throughout the Devonian epoch (415 million to 360 million years ago), providing new habitats for terrestrial creatures. Elkinsia, an early seed fern, developed seeds, especially in the late Devonian era.
Phanerozoic eon » Mesozoic era: This period lasted 252 million to 66 million years. Flowering plants first occur in the Triassic period (about 200 million years ago).
Phanerozoic eon » Cenozoic era: The “new life” epoch, which stretches from 66 million years ago to the present day, is the most recent geological epoch. The grasses first developed during this time period, about 40 million years ago. To withstand the low CO2 and dry conditions of the tropics, these plants and many other plant species developed a novel metabolic process.
Because they all include chloroplasts and a cell wall, green algae, fungus, and embryophytes are included in the original definition of plants. Algae and fungus, on the other hand, were finally assigned to their separate kingdoms.
Plants (i.e. Plantae sensu strictissimo) are multicellular organisms having cellulose-containing cell walls and chloroplasts for photosynthesis in the strictest meaning. The kingdom Plantae is made up of embryophytes, which include vascular plants, liverworts, mosses, and other fossil plants with similar characteristics.
Embryophytes and green algae are included in Plantae sensu stricto (“plants in a limited sense”) (Chlorophyta and Charophyta). This concept of plants is still commonly used today. They belong to the Viridiplantae (or Chlorobionta) group, which is also known as the green plants.
The following are the divisions of the kingdom Plantae sensu stricto: Chlorophyta, Charophyta, Marchantiophyta (liverworts), Anthocerotophyta (hornworts), Bryophyta (mosses), Lycopodiophyta (club mosses), Pteridophyta (ferns, whisk ferns, and horsetails), Cycadophyta (cycads), Ginkgophyta (ginkgo), Pinophyta (flowering plants).
Significance of Plants
Plants are necessary for the survival of many creatures since they are the food chain’s producers. They are capable of storing starch. They’re also a valuable source of minerals and chemicals.
Plants provide homes for a variety of creatures, e.g. insects and arboreal organisms. They are also the most important source of oxygen for aerobic creatures.
Medicinal qualities can be found in some plants. Plantain (Plantago major) leaves for decreasing inflammation and discomfort, and burdock (Arctium minus) roots and leaves for eczema and damaged skin are just a few of the many therapeutic plants.
Essential oils, pigments, resins, tannins, alkaloids, amber, waxes, cosmetics, plastics, rubber, varnish, lubricants, inks, and a variety of other goods are all made from plants.
Buildings, musical instruments, boats, and furniture are all made from plant-based wood. It’s also utilised in the production of paper.
Botany is the field of science that examines plants (or plant biology). A botanist is a specialist in this subject. Some of the disciplines of study comprise morphology, cytology, histology, physiology, ecology, evolution, taxonomy, and pathology. Sub-disciplines emerged as a result of the diversity of plant groupings, including:
1. Paleobotany is the science of studying fossil plants.
2. Algology is the study of algae.
3. Mycology is the study of fungi.
4. Bryology is the study of mosses, liverworts, and hornworts.
5. Pteridology is the science of ferns.
6. Pollen grains and spores are studied in palynology.
Applied botany is concerned with the commercial and economic applications of plants. Agriculture (for example, agronomy, horticulture, and plant breeding), forestry (for example, dendrology, wood technology), pharmaceutical botany, and landscape architecture are all included.
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