Biology - Lesson 3 (117)

Meristematic Tissues - Plants can grow continuously due to the activity of meristems, unspecialized tissues composed of dividing cells.

Plant tissue - A flowering plant can grow throughout its entire life because it possesses meristematic (embryonic) tissue:

• Meristematic tissue

• Epidermal Tissue

• Ground Tissue

• Vascular Tissue

Apical Meristems - Are located at the tips of roots and shoots, elongate shoots and roots, primary growth.

• Protoderm - Produces dermal tissue, forms the outer protective covering of a plant.

• Ground Meristem - Produces ground tissue, fills the interior of a plant.

• Procambium - Produces vascular tissue, transports water and nutrients and provides support.

Lateral Meristems - Add thickness to woody plants, a process called secondary growth.

• Vascular Cambium - Adds a layer of vascular tissue called secondary xylem (wood) and secondary phloem.

• Cork Cambium - Replaces the epidermis with periderm, which is thicker and tougher.

Intercalary Meristem - Are located at the internodes or the base of the leaves. The intercalary meristems help in increasing the length of the internode. This type of meristem occurs only in monocots, particularly grass. Through this growth, these plants are able to rapidly regrow leaves and elongate stems as an adaptive mechanism against herbivory.

Epidermal/Dermal Tissues - The entire body of both nonwoody (herbaceous) and young woody plants are made up of closely packed cells called epidermis.

Cuticle - The walls of epidermal cells exposed to air are covered with a waxy cuticle to minimize water loss, and to protect against bacteria and other organisms that might cause disease in plants.

Root Hairs - Long, slender projections certain epidermal cells develop in roots.

Trichomes - Epidermal cells produce hairs on the surfaces of stems, leaves, and reproductive organs to protect the plant from too much sun and to conserve moisture.

Guard Cells - Specialized epidermal cells in leaves facilitating gas exchange in shoots.

Stomata - A pair of guard cells surrounding microscopic pores which regulate gas exchange and water loss in leaves.

Periderm - Epidermis of young stems that replaces woody plants as it gets older.

Cork Cells - The major component of the periderm which are boxlike.

Cork Cambium - Over productions of cork cells in certain areas of the stem surface cause ridges and cracks to spear.

Ground Tissue - Forms the bulk of a flowering plant and contains parenchyma, collenchyma and sclerenchyma cells.

Parenchyma Cells - Most abundant type of plant tissue found in all organs but the least specialized. Their functions depend on the type of pigment they contain.

Collenchyma Cells - Like parenchyma cells except that they have thicker primary walls. The thickness is uneven and usually found in the corners of the cell.

Sclerenchyma Cells - Have thick secondary walls filled with a highly resistant organic substance called lignin that makes the walls tough and hard. Mostly non living and supports the mature regions.

Fibers - Long and slender structures and may be grouped in bundles. They are mostly found in vascular tissue, although they may be occasionally found in ground tissue.

Sclereids - (Stone cells) shorter than fibers and more varied in shape, are found in seed coats and nutshells. Responsible for the gritty structure of pears, as well as the hardness of nuts and peach pits.

Vascular Tissues has two types:

Xylem – Transports water and minerals from the roots to the leaves.

Tracheids – Form a less obvious means of transport (elongated with tapered ends). Water can move across the end walls and side walls because there are pits, or depressions, where the secondary walls do not form.

Vessel elements – Larger, may have perforation plates in their end walls, and are arranged to form a continuous vessel for water and mineral transport. Both types of conducting cells are hollow and nonliving.

Phloem – Transports sucrose and other organic compounds, usually from the leaves to the roots.

Sieve Tube Members – Specialized elongated parenchyma cells which are arranged end to end forming a continuous column.

Companion Cells – Has a nucleus and helps the sieve tube members carry out their function.

Fibers – Lend supports to the phloem.

Parenchyma

1. Epithelial Cells - Consists of tightly packed cells that form a continuous layer. Covers surfaces and lines body cavities and therefore provides protective function.

Tight Junction - Form impermeable barrier between cells.

Adhesion Junctions - Add strength and allow epithelial cells to stretch and bend.

Gap Junctions - Permit the passage of molecules between two adjacent cells.

Basement Membrane – Thin layer of various types of proteins that anchor the epithelium to the extracellular matrix which is often a type of connective tissue.

Types of Epithelial Tissue
Simple Epithelium – Single layer of cells and is classified according to the shape of cells.

Squamous epithelium – Composed of flattened cells and found in lining blood vessels and the air sacs of lungs.

Cuboidal Epithelium – Contains cube-shaped cells and found lining the kidney tubules and various glands.

Columnar Epithelium – Resembles rectangular pillars found in lining the digestive tract. Ciliated columnar epithelium is found lining the oviducts where it propels the egg towards the uterus.

Pseudo Stratified Epithelium – Appears to be layered, but true layers do not appear because each cell is attached to the basement membrane.

Stratified Epithelium – Made up of more than one layer of cells. Only the bottom layer touches the basement membrane.

Glandular Epithelium – Kind of epithelium that secretes a product. A gland can be a single – cell gland is the mucus – secreting goblet cells found within the columnar epithelium lining the digestive tract.

Exocrine Glands – Secretes their products into ducts.

Endocrine glands – Have no ducts and secrete their products directly into the blood stream.

2. Connective Tissue - Most abundant and widely distributed tissue in complex animals.

Specialized Cells

Ground Substance – Found in between the cells, is a noncellular material that varies in consistency from solid to semifluid to fluid.

Protein Fibers

White Collagen Fibers – Contain collagen – protein that gives them flexibility and strength.

Reticular Fibers – Contain very thin collagen fibers which are highly branched and form delicate supporting networks.

Yellow Elastic Fibers – Contains elastin, protein that is not long as strong as collagen but is more elastic.

Connective Tissue Matrix - The ground substance, together with the fibers.

The Three Categories of Connective Tissues

• Fibrous

  • Loose Fibrous Connective Tissue

  • Dense Fibrous Connective Tissue

• Supportive

• Fluid

Loose Fibrous Connective Tissue - Has fibroblasts and collagen fibers widely scattered in its matrix. 

• Adipose Tissue – Loose connective tissue composed mostly of enlarged fat-storing fibroblast called adipocytes. It also serves as the body’s primary energy reservoir.

Dense Fibrous Connective Tissue - Contains many collagen fibers that are tightly packed together.

Supportive Connective Tissue - This type of tissue includes cartilage and bones which are the two main supportive connective tissues that provide structure, shape and protection, and leverage for movement.

• Cartilage - Generally more flexible than bone because its matrix lacks calcium deposits. Contains cells that lie in small chambers called lacunae which are separated by a solid but flexible matrix. It heals very slowly because it lacks a direct blood supply

  • Hyaline cartilage – most common cartilage containing only very fine collagen fibers. This type of cartilage with a white translucent matrix is found in the nose, at the ends of the long bones and the ribs, and walls of the respiratory passages.

  • Elastic Cartilage – has more fibers making it more flexible than hyaline cartilage. It is found in the framework of the outer ear.

  • Fibro Cartilage – has a matrix containing strong collagen fibers.

• Bone - Has an extremely hard matrix made up mostly of calcium salts deposited among protein fibers especially collagen fibers.

  • Compact bone – consists of cylindrical structural units called osteons (Harvesian system).

    • Lacunae - Spaces bone cells (osteocytes) are found in between the rings of matrix.

  • Spongy bone – found at the ends of a long bone, contains numerous bony bars and plates separated by irregular spaces.

Fluid Connective Tissue - Blood, consisting of formed elements and plasma, is a fluid connective tissue located in blood vessels. Formed elements of blood consist of many kinds of blood cells and the plates.

• Red Blood Cells – Small biconcave disk-shaped cells without nuclei. They contain red pigment called hemoglobin which is made up of protein globin and a complex iron – containing heme.

• White Blood Cells – Much larger than red blood cells and contain nuclei which when stained typically looks blue or purple.

• Platelets – Not complete cells but fragments of large cells present only in bone marrow. They stop bleeding by forming a plug that seals the blood vessels.

• Lymphocytes – Specialized white blood cells, which together with other cells, remove any foreign materials from the body by phagocytosis.

3. Muscular Tissue - It is composed of cell muscle fibers that contain actin and myosin filaments. The interaction between these two protein filaments account for the movement of body parts. As muscles contact, body heat is generated.

Skeletal Muscle – Made up of long and cylindrical muscle fibers that sometimes run the entire length of the muscle. It is a voluntary muscle because it is under the control of the will.

Smooth Muscle – Made up of spindle – shaped mononucleated cells which are not under voluntary control.

Cardiac Muscle – Found only in the heart, has both features of skeletal and smooth muscles. It has striations, but its contractions are involuntary like the smooth muscles. It has a single and centrally located nucleus.

4. Nervous Tissue - It is made up of specialized signaling cells called neurons and supporting cells called neuroglia. About a trillion neurons are present in an average human body. The nervous system conducts signal termed nerve impulses throughout the body.

Neurons - Contains three parts, cell body, dendrites, and axon.

Cell Body – Processes such as the dendrites and the axons.

Dendrites – Conducts signals toward the cell's body, while axons are covered by a fatty substance called myelin.

Axon – Conducts signals away from the cell body.

Neuroglia - More than half of the brain volume is made up of these cells which functions to support, nourish and protect neurons.

Microglia – Gives support, as well as protection to the neurons by engulfing bacterial and cellular debris.

Astrocytes – Provide nutrients to neurons and produce a hormone known as glial cell – derived growth factor which is being studied as a possible treatment for Parkinson’s diseases caused by neuron degeneration.

Oligodendrocytes – Form myelin in the brain.

The nervous system carries out three major functions:

1. Sensory input

2. Integration of data

3. Motor output

Cell Modification - A process that occurs after cell division where the newly formed cells are structurally modified so that they can perform their function effectively.

Plant Cell Modifications

Succulent leaves - Of century plant (Agave), aloes, sedums, and desert plants, which are thick and fleshy, store water to enable them to survive long periods of drought and semidesert conditions.

Tendrils - (Modified leaf petioles, veins, or stipules), growing in climbing plants like garden peas, bitter gourd and cucumber, can coil around support for anchorage.

Brightly Coloured - To help attract pollinators.

Tubular or Vase - Shaped leaves of Pitcher plants secrete a fluid for digesting insects falling into their cavities.

Lateral roots - Of mangrove trees growing in swamps produce pneumatophores (upright conical growths) that aerate the submerge roots.

Adventitious Roots - (Called brace or prop roots) that develop from the stem or even from the leaves, such as in pandan or corn, grow into the ground to help underground roots support the stem.

Animal Cell Modifications

Microvilli – Finger-like projections extending from the free surface of epithelial cells that increase the surface area across which substances are absorbed.

Fimbriae – Finger-like extensions from the oviduct near the ovary that help to propel the released ova towards the fallopian tube.

Alveoli – Microscopic, grapelike air sacs found at the tip of the bronchioles in the lungs that provide tremendous surface area for gas exchange during respiration.

Goblet cell – A glandular, modified simple columnar epithelial cell that secretes gel-forming mucins, the major components of mucus.

Red Blood Cells – A biconcave disk-shaped cell that provides more surface area for gas exchange; absence of its nucleus in mature red blood cells give more space for the hemoglobin.

White Blood Cells – Also called leukocytes, contain enzymes and other proteins needed to protect the body against both infectious diseases and foreign invaders.

Neuron – A specialized cell with three parts:

1. Dendrites

2. Cell body

3. Axon

Sperm Cell – Has lots of mitochondria that will produce the energy needed to propel its flagellum towards the egg cell during fertilization; and contains the enzyme needed to penetrate the thick membrane surrounding the egg and deliver its genetic material.

Ciliated Epithelium – Located in the upper airways sweeps mucus with inhaled particles away from the lungs. Cilia in the oviduct move an egg towards the uterus.

Stem Cells – Unique cells of the body in that they are unspecialized and have the ability to develop into specialized cells for specific organs or to develop into tissues.

Cancer Cells - Results from the development of abnormal properties in normal cells that enable them to divide uncontrollably and spread to other locations.

• Apoptosis - Programmed cell death.

Endothelial Cells - Form the inner lining of cardiovascular system and lymphatic system structures. These cells make up the inner layer of blood vessels, lymphatic vessels, and organs including the brain, lungs, skin, and heart.

Cilia - An organelle found in eukaryotic cells. These are slender protuberances that project from the much larger cell body.

• Motile Cilia - Usually present on a cell's surface in large numbers and beat in coordinated waves. 

• Non-Motile (Primary Cilia) - Usually occurs one per cell; all mammalian cells have a single non-motile primary cilium. For example, sensory organs like eyes and nose.

Mechanoreceptors - A primary cilium extends from the apical surface of the epithelial cells lining the kidney tubules and monitors the flow of fluid through the tubules.

Chemoreceptors - Detect odors by receptors on the primary cilium of olfactory neurons.

Photoreceptors - The outer segment of the rods in the vertebrate retina is also derived from a primary cilium.

Flagella - A tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and functions in locomotion.

Sex Cells/Gametes - play a crucial role in the reproductive process of organisms, characterized as haploid, meaning they only contain half of the chromosomes found in normal somatic cells. 

(Somatic Cells = 2 Sets/46 chromosomes: Sex cells = 1 Set/23 chromosomes).