Introductions

There are plants of all shapes and sizes in the Plantae kingdom, which encompasses everything from microscopic mosses to enormous trees. Although there is a wide range of plants, they are all multicellular and eukaryotic (i.e., each cell possesses a membrane-bound nucleus that contains the chromosomes). Chlorophyll A and B and carotenoids are common pigments in plants, which play a key role in photosynthesis by turning sunlight into chemical energy. As a result of this, most plants are self-sustaining (autotrophic) and store surplus food as macromolecules of starch. The few plants that are not autotrophic have lost their pigments and have to rely on other creatures for their nourishment. Even though plants do not move, some develop cells (gametes) that are pushed by flagella. Cell walls are made of carbohydrate cellulose, and plasmodesmata, minute strands of cytoplasm, connect neighboring cells. Many plants can develop indefinitely at meristems, which are confined regions of cell division. A key component of animal protein, nitrogen, is essential for plant survival; however, plants can use inorganic forms of nitrogen (N), such as nitrate and ammonia, which are made available to plants by microbes or the industrial manufacturing of fertilizers, and the element sulfur (S).

Angiosperm life cycle

A typical angiosperm's life cycle. There is a sporophyte stage and a gametophyte stage in the angiosperm life cycle. Each of the cells in the sporophyte body has two copies of the chromosomes, indicating that the cells are diploid, or 2n, and so represent the normal plant body found in an angiosperm. To prepare for reproduction, sporophyte cells undergo meiosis, resulting in gametophytic reproductive cells with only half the number of chromosomes as the sporophyte's (i.e., haploid, or n). Microgametophytes (also known as pollen grains) are two-celled microgametophytes that germinate and produce haploid sperm. Embryos are produced by an eight-celled megagametophyte. Once an egg is fertilized and an embryo is formed, the process is known as fertilization. The ovule becomes a seed after fertilization, and the ovary becomes a fruit after fertilization.

Structure, growth, and development

The atmosphere provides the vast majority of the plant's solid substance. Most plants use the energy in the sunshine to transform atmospheric carbon dioxide and water into simple sugars through the process of photosynthesis. The plant's primary structural component is constructed from the sugars that are employed as building blocks. A crucial component of this process is plant leaves and other portions of the plant that contain chlorophyll, a green, magnesium-containing pigment. In contrast, parasitic plants rely on the resources of their host to obtain the nutrients and other building blocks necessary for their metabolism and growth.

Soil provides a variety of essential nutrients to plants, but plants mostly use it for support and water. Soil also contains nitrogen, phosphorus, potassium, and magnesium compounds. Carnivorous plants, like epiphytes and lithophytes, feed on insects and nearby debris to replenish their nutrient needs, while epiphytic and lithophyte plants depend on air and neighboring debris for nutrition. Most plants need oxygen for respiration in the air and around their roots (soil gas) to thrive. As a source of energy, plants utilize oxygen and glucose (which may be derived from stored starch). Mangroves and reed (Phragmites australis) are examples of specialized vascular plants that can thrive with their roots under anoxic circumstances, while other plants, such as submerged aquatics, use oxygen dissolved in the surrounding water.

Factors affecting growth

A plant's growth is governed by its genome. For example, certain wheat kinds or genotypes develop in 110 days, whereas others mature in 155 days under the same climatic conditions.

Temperature, water availability, light, carbon dioxide, and nutrients in the soil are all elements that affect plant growth. The plant's growth and development will be affected if any of these environmental factors change.

Plant growth is also affected by biotic variables. Etiolation and chlorosis can occur in plants when they get overcrowded to the point that no one individual can provide normal development. Grazing animals, poor soil quality, a lack of mycorrhizal fungi, and pests or diseases, such as those caused by bacteria, fungus, viruses, and nematodes, can all hinder plant growth.

It's typical to see seasonal populations of simple plants like algae, which have short life spans as individual plants. During their second year of growth, biennial plants produce seeds, while perennials live for multiple years of growth before reproducing annually after they reach reproductive maturity. These classifications are frequently influenced by the local climate and other natural conditions. In warmer climates, plants that are annual in alpine or temperate zones might be biennial or perennial. There are two types of perennials in the vascular plant kingdom: evergreens, which retain their leaves throughout the year, and deciduous trees and shrubs, which shed their leaves for part of the year. Many tropical plants shed their leaves throughout the dry season of the year in temperate and boreal climes.

Plant growth rates are highly unpredictable. When it comes to trees, the most majority of them grow at between 0.025–0.250 millimeters (mm/h) each hour. Kudzu, for example, may grow at a rate of 12.5 millimeters per hour because it does not require the production of substantial supporting tissue.

Heat shock proteins and carbohydrates help plants fend off the effects of frost and dehydration (sucrose is common). Desiccation and freezing prevent protein aggregate formation by inducing the production of the LEA (Late Embryogenesis Abundant) protein.

DNA damage and repair

A wide variety of biotic and abiotic stressors are constantly exerting pressure on plants. Damage to DNA can occur either directly or indirectly as a result of the formation of reactive oxygen species during times of stress. Plants can respond to DNA damage in a way that is crucial to the stability of their genome. During seed germination, the DNA damage response is especially critical because seed quality degrades over time as a result of DNA damage build-up. To deal with the accumulated DNA damage, repair activities are engaged during germination. The repair of DNA breaks, both single and double-stranded, is possible in particular. An important role is played by ATM, the DNA checkpoint kinase, in the integration of germination and DNA repair responses.

Plant cells

Large water-filled central vacuoles, chloroplasts, and hard cell walls composed of cellulose, hemicellulose, and pectin define plant cells. A phragmoplast is formed in the last phases of cell division for the production of a cell plate, which is another distinguishing feature of cell division. Similar to animal cells, plant cells undergo differentiation and multiplication to produce a wide variety of cell types. Meristematic cells are totipotent and can develop into vascular, storage, protective (e.g., epidermal layer), or reproductive tissues, with more primitive plants lacking specific tissue types.

Physiology

Photosynthesis

When a plant photosynthesizes, it means that it uses light energy to create its food molecules. The pigment chlorophyll is the fundamental means by which plants capture light energy. Chlorophyll a and chlorophyll b are the two types of chlorophyll found in all green plants. Red and brown algae do not have these colors.{\displaystyle {\ce {6CO2{}+6H2O{}-[{\text{light}}]C6H12O6{}+6O2{}}}}

Immune system

A plant's nervous system uses cells to collect and convey information about light intensity and quality. A type of cell known as a bundle sheath cell is responsible for a chain reaction of signals to the entire plant when an incident light activates a chemical reaction in one leaf. For the first time, researchers from Poland's Warsaw University of Life Sciences have discovered that plants have an innate ability to adapt their immune systems to seasonal threats. Recognition of conserved microbial fingerprints is achieved by the use of pattern-recognition receptors in plants an immunological response is elicited as a result of the recognition. Both Arabidopsis thaliana (XA21, 1995) and rice (XA21, 1995) included the first plant receptors for conserved microbial signatures (FLS2, 2000). Pathogen effectors with a wide range of molecular variations are recognized by immunological receptors found in plants. Included in this class of proteins are NBS-LRR proteins.

Internal distribution

Xylem and phloem are two specialized structures of vascular plants that carry nutrients between the plant's many components. Also, they've set up a shop to suck up water and minerals from the ground. Water and minerals are transported from the roots by the xylem, whereas sugars and other nutrients are obtained from the atmosphere by the phloem, which is the plant's thinnest substance. Most plants use the energy in the sunshine to transform atmospheric carbon dioxide and water into simple sugars through the process of photosynthesis. The plant's primary structural component is constructed from the sugars that are employed as building blocks. For this process to take place, chlorophyll, a green-colored, magnesium-containing pigment, must be present in plant leaves, as well as in other sections of the plant. In contrast, parasitic plants rely on the resources of their host to obtain the nutrients and other building blocks necessary for their metabolism and growth.

For the most part, plants rely on soil for support and water (quantitatively), but they also get compounds of nitrogen and phosphorus from the soil, as well as potassium, magnesium, and other elemental nutrients. Carnivorous plants, like epiphytes and lithophytes, feed on insects and nearby debris to replenish their nutrient needs, while epiphytic and lithophyte plants depend on air and neighboring debris for nutrition. Oxygen in the atmosphere and surrounding the roots (soil gas) is also necessary for the majority of plants to thrive. As a source of energy, plants utilize oxygen and glucose (which may be derived from stored starch). Mangroves and reed (Phragmites australis) are examples of specialized vascular plants that can thrive with their roots under anoxic circumstances, while other plants, such as submerged aquatics, use oxygen dissolved in the surrounding water.

Effects of freezing

When water freezes inside cells (intracellularly) or outside cells (intercellularly), the effects for the plant are significantly different. Even if a plant's tissues and cells are hardy enough to withstand intracellular freezing, it rarely occurs in nature since cooling rates aren't high enough to support it. Intracellular ice formation normally requires cooling rates of several degrees Celsius per minute. Intercellular ice segregation occurs at cooling rates of a few degrees Celsius per hour. Depending on the tissue's toughness, this may or may not be fatal. The water in the intercellular spaces of plant tissue freezes first at freezing temperatures, while the water may remain unfrozen until temperatures fall below 7 °C (19 °F) in the tissue. Cells begin to shrink when water is absorbed by the separated ice, and they experience freeze-drying as a result. Freezing injury is now thought to be the result of severe dehydration.

Plant cell structure

Large water-filled central vacuoles, chloroplasts, and hard cell walls composed of cellulose, hemicellulose, and pectin define plant cells. A phragmoplast is formed in the last phases of cell division for the production of a cell plate, which is another distinguishing feature of cell division. Similar to animal cells, plant cells undergo differentiation and multiplication to produce a wide variety of cell types. Cells that are totipotent meristematic can be reprogrammed to become vascular, storage, or protective tissues.