Biological World

  S tructure of Lysosome Lysosomes are small, spherical, membrane-bound cell organelles mainly found in animal cells. They are involved in intracellular digestion and removal of waste materials. Lysosomes contain many hydrolytic enzymes, so they are commonly called the digestive bags of the cell. They are also known as suicidal bags because, under certain conditions, their enzymes may digest the cell’s own components. Lysosomes were discovered by Christian de Duve in 1955. They are present in large numbers in cells that show active digestion, such as white blood cells, liver cells, and kidney cells. Lysosomes are generally absent or less prominent in mature plant cells because vacuoles perform similar functions in plants. Lysosomes are usually spherical or oval in shape. Their size varies from about 0.1 to 1.2 micrometers , depending on the type of cell and its physiological activity. They are formed by the Golgi apparatus . The digestive enzymes of lysosomes are first synthesi...

  Aquaporins Aquaporins are integral membrane proteins that form special channels for the rapid movement of water molecules across biological membranes. They are also known as water channel proteins. These proteins are present in plants, animals, bacteria, and many other organisms. Aquaporins help water move across the plasma membrane and tonoplast without allowing ions and most solutes to pass through. Structurally, aquaporins are embedded in the membrane and form narrow pores. Water molecules pass through these pores in a single-file arrangement. The pore is very selective, so charged particles such as protons and ions cannot pass through. This selectivity is important because it maintains the ionic balance and electrochemical gradient of the cell. In plants, aquaporins are very important for water absorption and transport. They help roots absorb water from the soil and assist in the movement of water from cell to cell. They are also involved in maintaining cell turgor pressure, ...

  Comparison of Internal Structure of Leaf of Selaginella and Lycopodium Feature Selaginell a Leaf Lycopodium Leaf Leaf type Microphyllous leaf; generally small, simple, and ligulate. Microphyllous leaf; simple and usually eligulate. General arrangement Leaves are commonly arranged in four rows and may be unequal in size, especially in dorsiventral species. Leaves are usually small, simple, equal in size, and commonly arranged spirally around the stem. Epidermis Single-layered epidermis is present on both surfaces and is covered by a thin cuticle. Single-layered epidermis is present on both surfaces and is covered by a cuticle. Cuticle Cuticle is generally thin, but it may vary according to habitat. Cuticle is usually well developed and may be thicker in xerophytic species. Stomata Stomata are present, usually more common on the lower/abaxial surface. Stomata are present, commonly on the lower surface or sometimes on both surfaces depending on specie...

  Comparison of Internal Structure of Root of Selaginella and Lycopodium   Feature Selaginella root Lycopodium root Root origin Roots commonly arise from rhizophores; they are adventitious in nature. Roots arise adventitiously from the stem or rhizome. Root system Usually delicate, dichotomously branched roots. Adventitious roots, often dichotomously branched and comparatively firm. Epidermis / piliferous layer Outermost single-layered piliferous layer; root hairs may be present in young roots. Single-layered epidermis or piliferous layer; root hairs may be present in young roots. Cuticle Cuticle is absent or very thin because it is a root. Cuticle is absent or very thin. Cortex Cortex is well developed and usually parenchymatous, though some cells may become thic...

  Comparison of Internal Structure of Stem of Selaginella and Lycopodium Characteristics Selaginella Stem Lycopodium Stem Plant group Heterosporous lycophyte Homosporous lycophyte Stem nature Usually delicate and branched Usually firm and dichotomously branched Epidermis Single-layered epidermis with cuticle Single-layered epidermis with cuticle Stomata on stem May be present in young stem Usually few or absent on stem Cortex Well-developed cortex; often differentiated into outer sclerenchymatous and inner parenchymatous regions Broad cortex; commonly differentiated into outer, middle, and inner regions Outer cortex Generally sclerenchymatous and provides mechanical support Often sclerenchymatous or compact parenchymatous Inner cortex Usu...