14.1 The Plant Kingdom

• There is a diversity of plants including oils and dates.
• Human and animal populations are fed wheat.
• The cotton flower's fibers are turned into clothing or paper.
• The showy opium poppy is a source of potent opiate compounds and is valued both as an ornamental flower and as a source of potent opiate compounds.

• All plants are descendants of a single common ancestor according to current evolutionary thought.
• The ancestors of modern plants were constrained by the transition from water to land.
• To avoid drying out, plants had to evolve strategies, such as dispersal of reproductive cells in air, for structural support, and to filter sunlight.
• Full independence from water was not achieved in all plants, and most seedless plants still need a moist environment.

• Plants are a diverse group of organisms.
• There are hundreds of thousands of plants.
• There are 260,000 plants that produce seeds.
• The plant kingdom includes mosses, ferns, conifers, and flowering plants.

• The plant kingdom has mostly photosynthetic organisms, but a few have lost the ability to photosynthesize.

• The process of photosynthesis uses a plant.
• Plants have cell walls.
• Plants have different methods of reproduction.
• Plants grow body mass until they die, meaning they don't have a final body form.

• As organisms adapt to life on land, they have to contend with a number of challenges.
• The majority of the chemical reactions of metabolism take place in the cell's interior, which is a watery soup.
• Desiccation is a constant danger for organisms exposed to air.
• When parts of a plant are close to water, their aerial structures are likely to dry out.
• Water helps organisms live in aquatic habitats.
• Plants need structural support in air, a medium that does not give the same lift.
• Swimming is no longer possible for the male and female gametes.
• Gametes and zygotes need to be protected from drying out.
• The successful land plants adapted to all of the challenges.
• Some species left the water and went on to conquer the driest environments on Earth, while others didn't move far from an aquatic environment.

• Life on land offers a number of advantages.
• Sun is abundant.
• The water in the water column above does not affect the quality of light absorbed by the photosynthetic pigment, chlorophyll.
• The concentration of carbon dioxide in air is higher than in water.
• Until dry land was colonized by animals, there was no threat to the well-being of plants.
• The situation changed when animals emerged from the water with abundant sources of food and water.
• Plants evolved strategies to deter predator: from thorns to toxic chemicals.

• Like the early land animals, the early land plants developed survival strategies to combat the effects of dry weather.
• One of the strategies is tolerance for dry weather.
• Mosses can dry out to a brown and brittle mat, but as soon as rain makes water available, mosses will soak it up and regain their green appearance.

• It is possible to colonize environments with high humidity.
• Ferns thrive in damp and cool places, such as the understory of temperate forests.
• Plants used resistance to desiccation rather than tolerance to move away from aquatic environments.
• These plants are able to survive in the driest environments on Earth because of their low water loss.

• Land plants have adapted to life on land and this has an effect on their diversity and predominance in the land.
• Alteration of 1 is one of the major adaptations found in many plants.

• A sporangium, a gametangium that produces haploid cells, and apical meristem tissue can be found in this OpenStax book.

• Alternation of generations is a description of a life cycle in which both haploid and diploid multicellular stages are present.

• Humans are diplontic.
• It can be the most obvious phase of the life cycle of the plant, as in the mosses, or it can occur in a tiny structure, such as a pollen grain in the higher plants.
• The collective term for the plant groups of mosses, liverworts, and hornworts is the sporophyte stage.
• Sequoias and pines have towering trees in their lifecycles.

• The term "spore in a vessel" refers to a reproductive sac that contains spores.

• The sporangia releases the spores in the environment.
• The sexes are separated at different points in the life cycle when two different types of spores are produced in land plants.
• The male and female gametophytes are called microspores because of their smaller size.
• In a few seedless plants and in all seed plants, Heterospory is observed.

• The haploid spore creates a multicellular gametophyte.

• The life cycle of a fern shows a variety of generations.

• The life cycle of a moss shows a variety of generations.

• The thick cell walls that surround the seeds of seedless plants and the pollen of seed plants are made of a tough substance known as sporopollenin.
• The yellow color of most pollen is due to the long chains of organic molecules in this substance.
• It is resistant to chemical and biological degradation.
• The existence of well-preserved fossils of pollen is explained by its toughness.

• Land plants need protection of the embryo.
• The embryo needs to be protected from desiccation.
• In both seedless and seed plants, the female gametophyte provides nutrition and the embryo is protected as it develops into the new generation of sporophyte.

• Gametangia are structures on the gametophytes of seedless plants in which gametes are produced.
• The male gametangium releases sperm.
• Many seedless plants have flagella that allow them to swim in a moist environment to the female gametangium.
• The embryo is inside the archegonium.

• The apical meristem is a cap of cells at the shoot tip or root tip made of undifferentiated cells.
• All the specialized tissues of the plant are created by meristematic cells.
• Light and water can be found in the shoots and roots, as well as minerals, which can be found in the roots.
• Cells that increase the diameter of stems and tree trunks are produced by a separate meristem.
• Apical meristems allow plants to grow in ways essential to their survival: upward to greater availability of sunlight, and downward into the soil to obtain water and essential minerals.

• An example of a plant in which the apical meristem gives rise to new shoots and root growth is the apple seedling.

• New organs and structures appeared as plants became independent of the constant presence of water.
• Early land plants did not grow above a few inches off the ground, and they competed for light on these low mats.
• Individual plants captured more light by growing taller.
• Land plants incorporated more rigid molecules in their stems because air offers less support than water.

• Plants had to evolve larger bodies in order to distribute water and solutes.
• The xylem and phloem tissues are in the vascular system.
• Xylem takes water and minerals from the soil up to the shoot and phloem takes food from the plant.
• The shoot in the soil was anchored by the root system that took up water and minerals.

• The leaves and stems of a land plant are covered with a waterproof cover called a cuticle.
• The intake of carbon dioxide is prevented by the cuticle.
• Plants that moved into drier habitats had open and close to regulate traffic of gases and water.

• Plants can't avoid predatory animals.
• They synthesise a large range of poisonous secondary metabolites, such as alkaloids, whose unpleasant smells and taste deter animals.
• These compounds can cause diseases and even death.

• As plants coevolved with animals, sweet and nutritious metabolites were developed to lure animals into providing valuable assistance in dispersal of pollen grains, fruit, or seeds.
• Plants have evolved with animals.

• Plants have adapted to life on land.

• fundamental questions of evolution include how organisms acquired traits that allow them to colonize new environments and how the modern environment is shaped.
• Paleobotany focuses on the study of extinct plants.
• Paleobotanists reconstituting the morphology of organisms that have long disappeared by analyzing specimen retrieved from field studies.
• They trace the evolution of plants by following the modifications in plant morphology and by identifying common ancestors that display the same traits.
• There are gaps in the path to the development of modern organisms.
• Fossils are formed when organisms are trapped in environments where their shapes are preserved.

• The age of the fossils and the nature of the environment are determined by paleobotanists.
• The delicate fossils and the layers in which they are found require great care.

• The use of analytical chemistry and molecular biology to study fossils is one of the most exciting recent developments in paleobotany.
• The environment free of oxygen is needed for the preservation of molecular structures since oxidation and degradation of material depends on the presence of oxygen.
• Oleanane, a compound that deters pests and appears to be unique to flowering plants, is an example of analytical chemistry and molecular biology being used.
• The current dates for the appearance of the first flowering plants are incorrect because Oleanane was recovered earlier.
• The most information comes from fossils of nucleic acids.
• They are compared to living organisms.
• Evolutionary relationships can be built through this analysis.

• Some paleobotanists don't agree with the conclusions drawn from the analysis of fossils.
• The chemical materials of interest degrade quickly when exposed to air and further manipulation.
• There is a high chance that the specimen will be contaminated with extraneous material.
• As technology is refined, the analysis of DNA from plants will provide valuable information on the evolution of plants and their adaptation to an ever-changing environment.

• Early in land plant evolution, the bryophytes, liverworts, mosses, and hornworts are seedless and nonvascular.
• The lycophytes, which include club mosses, and the pterophytes, which include horsetails, are similar to the first vascular plants.
• Plants that are seedless are referred to as lycophytes.
• They don't produce seeds because they don't have enough food to make them.
• The seed plants form the largest group of plants and dominate the landscape.