Plant

Trichomes (/ˈtraɪkoʊmz, ˈtrɪkoʊmz/; from Ancient Greek τρίχωμα (tríkhōma) 'hair') are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a plant is an indumentum, and the surface bearing them is said to be pubescent.

Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words χλωρός (khloros, "pale green") and φύλλον (phyllon, "leaf"). Chlorophyll allows plants to absorb energy from light. Those pigments are involved in oxygenic photosynthesis, as opposed to bacteriochlorophylls, related molecules found only in bacteria and involved in anoxygenic photosynthesis.

Chlorophylls absorb light most strongly in the blue portion of the electromagnetic spectrum as well as the red portion. Conversely, it is a poor absorber of green and near-green portions of the spectrum. Hence chlorophyll-containing tissues appear green because green light, diffusively reflected by structures like cell walls, is less absorbed. Two types of chlorophyll exist in the photosystems of green plants: chlorophyll a and b.

Variegation is the appearance of differently coloured zones in the foliage, flowers, and sometimes the stems and fruit of plants, granting a speckled, striped, or patchy appearance. The colors of the patches themselves vary from a slightly lighter shade of the natural coloration to yellow, to white, or other colors entirely such as red and pink. This is caused by varying levels and types of pigment, such as chlorophyll in leaves. Variegation can be caused by genetic mutations affecting pigment production, or by viral infections such as those resulting from mosaic viruses. Many plants are also naturally variegated, such as Goeppertia insignis. Most of these are herbaceous or climbing plants, and are most often species native to tropical rainforests.

Many species which are normally non-variegated are known to display variegation. Their appearance is desirable to enthusiasts, and many such plants are propagated and sold as unique cultivars. However, in individuals where the variegation occurs in normally-photosynthetic cells, the lack of functioning chloroplasts can slow growth rate. Conversely, naturally-variegated plants derive benefits from their appearance, such as improved photosynthetic efficiency in low-light conditions and herbivore deterrence.

In botany, succulent plants, also known as succulents, are plants with parts that are thickened, fleshy, and engorged, usually to retain water in arid climates or soil conditions.

Succulents may store water in various structures, such as leaves and stems. The water content of some succulent organs can get up to 90–95%, such as Glottiphyllum semicyllindricum and Mesembryanthemum barkleyii. Some definitions also include roots, thus geophytes that survive unfavorable periods by dying back to underground storage organs (caudex) may be regarded as succulents. The habitats of these water-preserving plants are often in areas with high temperatures and low rainfall, such as deserts, but succulents may be found even in alpine ecosystems growing in rocky or sandy soil. Succulents are characterized by their ability to thrive on limited water sources, such as mist and dew, which makes them equipped to survive in ecosystems that contain scarce water sources.

Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (/braɪˈɒfətə/, /ˌbraɪ.əˈfaɪtə/) sensu stricto. Bryophyta (sensu lato, Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and hornworts. Mosses typically form dense green clumps or mats, often in damp or shady locations. The individual plants are usually composed of simple leaves that are generally only one cell thick, attached to a stem that may be branched or unbranched and has only a limited role in conducting water and nutrients. Although some species have conducting tissues, these are generally poorly developed and structurally different from similar tissue found in vascular plants. Mosses do not have seeds and after fertilisation develop sporophytes with unbranched stalks topped with single capsules containing spores. They are typically 0.2–10 cm (0.1–3.9 in) tall, though some species are much larger. Dawsonia superba, the tallest moss in the world, can grow to 60 cm (24 in) in height. There are approximately 12,000 species.

Mosses are commonly confused with liverworts, hornworts and lichens. Although often described as non-vascular plants, many mosses have advanced vascular systems. Like liverworts and hornworts, the haploid gametophyte generation of mosses is the dominant phase of the life cycle. This contrasts with the pattern in all vascular plants (seed plants and pteridophytes), where the diploid sporophyte generation is dominant. Lichens may superficially resemble mosses, and sometimes have common names that include the word "moss" (e.g., "reindeer moss" or "Iceland moss"), but they are fungal symbioses and not related to mosses.

Polyester is a category of polymers that contain one or two ester linkages in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include some naturally occurring chemicals, such as those found in plants and insects. Natural polyesters and a few synthetic ones are biodegradable, but most synthetic polyesters are not. Synthetic polyesters are used extensively in clothing.

Polyester fibers are sometimes spun together with natural fibers to produce a cloth with blended properties. Cotton-polyester blends can be strong, wrinkle- and tear-resistant, and reduce shrinking. Synthetic fibers using polyester have high water, wind, and environmental resistance compared to plant-derived fibers. They are less fire-resistant and can melt when ignited.

A neuron (American English), neurone (British English), or nerve cell, is an excitable cell that fires electric signals called action potentials across a neural network in the nervous system. They are located in the nervous system and help to receive and conduct impulses. Neurons communicate with other cells via synapses, which are specialized connections that commonly use minute amounts of chemical neurotransmitters to pass the electric signal from the presynaptic neuron to the target cell through the synaptic gap.

Neurons are the main components of nervous tissue in all animals except sponges and placozoans. Plants and fungi do not have nerve cells. Molecular evidence suggests that the ability to generate electric signals first appeared in evolution some 700 to 800 million years ago, during the Tonian period. Predecessors of neurons were the peptidergic secretory cells. They eventually gained new gene modules which enabled cells to create post-synaptic scaffolds and ion channels that generate fast electrical signals. The ability to generate electric signals was a key innovation in the evolution of the nervous system.

The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants.

In land animals, the respiratory surface is internalized as linings of the lungs. Gas exchange in the lungs occurs in millions of small air sacs. In mammals and reptiles, these are called alveoli, and in birds, they are known as atria. These microscopic air sacs have a rich blood supply, bringing the air into close contact with the blood. A system of airways, or hollow tubes, allow the air sacs to interface with the external environment; the largest of these is the trachea, which branches in the middle of the chest into the two main bronchi, which enter the lungs and branch into progressively narrower secondary and tertiary bronchi, which in turn branch into numerous smaller tubes known as the bronchioles in mammals and reptiles. In birds, the bronchioles are termed parabronchi. The bronchioles, or parabronchi, generally open into the microscopic alveoli (in mammals) and atria (in birds). Air has to be pumped from the environment into the alveoli or atria by the process of breathing which involves the muscles of respiration.

This list of life sciences comprises the branches of science that involve the scientific study of life — such as animals (including human beings), microorganisms, and plants. This is one of the two major branches of natural science, the other being physical science, which is concerned with non-living matter. Biology is the overall natural science that studies life, with the other life sciences as its sub-disciplines.

Some life sciences focus on a specific type of organism. For example, zoology is the study of animals, while botany is the study of plants. Other life sciences focus on aspects common to all or many life forms, such as anatomy and genetics. Some focus on the micro scale (e.g., molecular biology, biochemistry), while others focus on larger scales (e.g., cytology, immunology, ethology, pharmacy, ecology). Another major branch of life sciences involves understanding the mind—neuroscience. Life-science discoveries are helpful in improving the quality and standard of life and have applications in health, agriculture, medicine, and the pharmaceutical and food science industries. For example, they have provided information on certain diseases, which has helped in the understanding of human health.

The Cretaceous–Paleogene (K–Pg) extinction event, formerly known as the Cretaceous-Tertiary (K–T) extinction event, was a major mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event caused the extinction of all non-avian dinosaurs. Most other tetrapods weighing more than 25 kg (55 lb) also became extinct, with the exception of some ectothermic species such as sea turtles and crocodilians. It marked the end of the Cretaceous period, and with it the Mesozoic era, while heralding the beginning of the current geological era, the Cenozoic Era. In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary or K–T boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows unusually high levels of the metal iridium, which is more common in asteroids than in the Earth's crust.

As originally proposed in 1980 by a team of scientists led by Luis Alvarez and his son Walter, it is now generally thought that the K–Pg extinction resulted from the impact of a massive asteroid 10 to 15 km (6 to 9 mi) wide, 66 million years ago, causing the Chicxulub impact crater and devastating the global environment, mainly through a lingering impact winter which halted photosynthesis in plants and plankton. The impact hypothesis, also known as the Alvarez hypothesis, was bolstered by the discovery of the 180 km (112 mi) Chicxulub crater in the Gulf of Mexico's Yucatán Peninsula in the early 1990s. The temporal match between the ejecta layer, and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations (for example, darkness and cooling), lead to the conclusion that the Chicxulub impact triggered the mass extinction. A 2016 drilling project into the Chicxulub peak ring confirmed that the peak ring comprised granite ejected within minutes from deep in the Earth, but contained hardly any gypsum, the usual sulfate-containing sea floor rock in the region: the gypsum would have vaporized and dispersed as an aerosol into the atmosphere, causing longer-term effects on the climate and food chain. In October 2019, researchers proposed the mechanisms of the mass extinction, arguing that the Chicxulub asteroid impact event rapidly acidified the oceans and produced long-lasting effects on the climate.