Category: Biology Second Paper Lecture Sheet

Living gymnosperms are divided into 4 categories.
1. Ginkgophyta: Ginkgo biloba is the only living species of Ginkgophyta. It is the world’s oldest seed plant that has survived on Earth with little change. Their leaves are large and fan-like. Their sperm are flagellated and motile. These plants greatly pollute the environment. They are disease and insect resistant.
2. Cycadophyta: Plants of Cycadophyta division are called cycads. This 200 million year old division survives today with 100 species. They are woody plants like palm trees. Their leaves resemble leathery feathers. Their sperm have flagella. They are widespread in the equatorial region. They grow in dry arid and wet wetlands. The division Cycadophyta consists of three classes. Cycadofilicales, Bennettitales and Cycadales. Zamia pygmaea cycad is the smallest gymnosperm plant in the world. Dr. Siddique Publications
3. Coniferophyta: Coniferophyta contains 550 species in 6 families. The temperate Northern Hemisphere has conifer forests. Russia has conifer forests. The world’s largest conifer forest is located in Siberia and is the world’s largest biome. Bristlecone pine is the oldest tree in the world. Its age is 5000 years. It is found in Navana and California. The tallest trees in the world are Hyperion (Sequoia sempervirens) at ± 400 feet and Coast Redwood (Sequoia gigantea) at 324 feet.
4. Gnetophyta: There are about 70 species in the Gnetophyta division. They have most similarities with herbaceous plants. Their leaves are similar to herbaceous plants. They have vessels in their xylem and spermatozoa are without flagella. The Welwitschia plant has two leaves and flower-like pods (Welwitschia is found in the Namibian desert). Double fertilization occurs in Ephedra plants of this category. The respiratory medicine ephedrine is obtained from the Ephedra plant.

Gymnosperms are always terrestrial. They carry frosty features. There are about 12 genera, 83 genera and 721 (some say 1080) species of gymnosperms in the world. 5 species of gymnosperms grow in Bangladesh. Cycas pectinata grows in Bariyadala Hills of Chittagong, Podocarpus nerifolius (Bamboo leaf) grows in Chittagong, Hill Chittagong and Sylhet, Gnetum grows in Chittagong, Hill Chittagong, Sylhet and Cox’s Bazar and Pinus carribeana grows in Chittagong. 3 species of Gnetum grow in Bangladesh. Gnetum latifolium, Gnetum montenum and Gnetum oblongum. Some gymnosperms are Pinus, Aurucaria, Cupressus, Thuja etc.

In 1825, Robert Brown separated gymnosperms from gymnosperms. The father of botany, Theophrastus, first used Gymnosperm in his Inquiry into Plants. Gymnosperms originated in the Devonian Period of the Paleozoic Era 300 million years ago and spread across the globe during the Mesozoic Era. The tallest trees in the world are Hyperion (Sequoia, Sequoia sempervirens) and General Sherman or Redwood Tree (Sequoia, Sequoia gigantea). The oldest tree, the bristlecone pine, is a gymnosperm. Zamia pygmaea is the world’s smallest gymnosperm.

The word Gymnosperm is formed from the Greek word Gymnos meaning naked or exposed and sperm meaning seed. The word gymnosperm means gymnosperm. Those plants that have flowers, seeds and fruits do not produce because the flower does not have an ovary, so the seeds are naked or expressed are called gymnosperms. The group of vascular plants that produce seeds is called Spermatophyta or green plants. Spermatophyta are divided into two subgroups. Gymnosperms and gymnosperms. All living gymnosperms are called living fossils. Gymnosperms were formerly called flowering plants, but are not today. Because the sporophylls of gymnosperms and the flowers of flowering plants have nothing in common.

Animals that excrete ammonia as excreta are called ammonotelic animals. For example – hydra, earthworms and some fish.

When the concentration of hydrogen ions in the body is low, it is called alkalosis. Alkalosis results in severe convulsions and death.

When the concentration of hydrogen ions in the body is high, it is called acidosis. In acidosis, people become unconscious and may die.

Different types of chemicals that prevent the change of fluid in the body are called buffers. Blood buffers are NaHCO3, Na2HPO4, KHCO3 etc.

If the acid level increases in the blood, the concentration of ions increases. Meanwhile, a Na+ ion enters the blood in exchange for an H+ ion. This results in a decrease in the concentration of H+ ions in the plasma and a change in the pH value of the blood. Again, when the blood alkalinization level increases, the rate of exchange of H+ and Na+ ions between the blood and the glomerular filtrate decreases and the blood pH changes.

When blood pH value (acidity) decreases, NH4+ is produced by the reaction of NH3 and hydrogen ion (H+) in plasma and renal tubule cells. This results in a decrease in the concentration of H+ ions in the plasma and a change in the pH value of the blood. Again, increasing alkalinity has the opposite reaction.