Plant Development I: Tissue differentiation and function | Biology
Describe the structure of the human body in terms of six levels of that enclose cytoplasm, a water-based cellular fluid together with a variety of tiny In multicellular organisms, including humans, all cells, tissues, organs, and organ systems. This book portrays the commonality of tissue micro-structure that dictates physiological function in various organs (microstructure-function relation). Tissue and. Cell, Basic structural and functional unit of a living organism. Tissue, Group of cells with similar structures, working together to perform a shared function. Organ .
For example, your digestive system is responsible for taking in and processing food, while your respiratory system—working with your circulatory system—is responsible for taking up oxygen and getting rid of carbon dioxide. The muscular and skeletal systems are crucial for movement; the reproductive system handles reproduction; and the excretory system gets rid of metabolic waste.
Because of their specialization, these different systems are dependent on each other. The cells that make up the digestive, muscular, skeletal, reproductive, and excretory systems all need oxygen from the respiratory system to function, and the cells of the respiratory system—as well as all the other systems—need nutrients and must get rid of metabolic wastes.
All the systems of the body work together to keep an organism up and running. Overview of body organization All living organisms are made up of one or more cells. Unicellular organisms, like amoebas, consist of only a single cell. Multicellular organisms, like people, are made up of many cells. Cells are considered the fundamental units of life.
The cells in complex multicellular organisms like people are organized into tissues, groups of similar cells that work together on a specific task. Organs are structures made up of two or more tissues organized to carry out a particular function, and groups of organs with related functions make up the different organ systems.
From left to right: For instance, the cells in the small intestine that absorb nutrients look very different from the muscle cells needed for body movement. The structure of the heart reflects its job of pumping blood throughout the body, while the structure of the lungs maximizes the efficiency with which they can take up oxygen and release carbon dioxide.
Types of tissues As we saw above, every organ is made up of two or more tissues, groups of similar cells that work together to perform a specific task. Humans—and other large multicellular animals—are made up of four basic tissue types: The four types of tissues are exemplified in nervous tissue, stratified squamous epithelial tissue, cardiac muscle tissue, and connective tissue in small intestine.
For instance, the outer layer of your skin is an epithelial tissue, and so is the lining of your small intestine. Epithelial cells are polarized, meaning that they have a top and a bottom side. The apical, top, side of an epithelial cell faces the inside of a cavity or the outside of a structure and is usually exposed to fluid or air. The basal, bottom, side faces the underlying cells. For instance, the apical sides of intestinal cells have finger-like structures that increase surface area for absorbing nutrients.
Image showing three cells lining the small intestine. Each cell contains a nucleus and is surrounded by a plasma membrane. The tops of the cells have microvilli that face the cavity from which substances will be absorbed.
Often, the cells are joined by specialized junctions that hold them tightly together to reduce leaks. Connective tissue Connective tissue consists of cells suspended in an extracellular matrix. In most cases, the matrix is made up of protein fibers like collagen and fibrin in a solid, liquid, or jellylike ground substance.
Connective tissue supports and, as the name suggests, connects other tissues. Loose connective tissue, show below, is the most common type of connective tissue. It's found throughout your body, and it supports organs and blood vessels and links epithelial tissues to the muscles underneath. Dense, or fibrous, connective tissue is found in tendons and ligaments, which connect muscles to bones and bones to each other, respectively.
Loose connective tissue is composed of loosely woven collagen and elastic fibers. The fibers and other components of the connective tissue matrix are secreted by fibroblasts. Specialized forms of connective tissue include adipose tissue—body fat—bone, cartilage, and bloodin which the extracellular matrix is a liquid called plasma.
Muscle tissue Muscle tissue is essential for keeping the body upright, allowing it to move, and even pumping blood and pushing food through the digestive tract. Muscle cells, often called muscle fibers, contain the proteins actin and myosin, which allow them to contract. There are three main types of muscle: From left to right. Smooth muscle cells, skeletal muscle cells, and cardiac muscle cells. Smooth muscle cells do not have striations, while skeletal muscle cells do. Cardiac muscle cells have striations, but, unlike the multinucleate skeletal cells, they have only one nucleus.
Cardiac muscle tissue also has intercalated discs, specialized regions running along the plasma membrane that join adjacent cardiac muscle cells and assist in passing an electrical impulse from cell to cell. Skeletal muscle is attached to bones by tendons, and it allows you to consciously control your movements.
For instance, the quads in your legs or biceps in your arms are skeletal muscle. Cardiac muscle is found only in the walls of the heart.
Like skeletal muscle, cardiac muscle is striated, or striped. But it's not under voluntary control, so—thankfully!
The individual fibers are connected by structures called intercalated disks, which allow them to contract in sync. A single vascular bundle always contains both xylem and phloem tissues. Xylem tissue transports water and nutrients from the roots to different parts of the plant, and includes vessel elements and tracheids, both of which are tubular, elongated cells that conduct water.
Tissues, organs, & organ systems
Tracheids are found in all types of vascular plants, but only angiosperms and a few other specific plants have vessel elements. Tracheids and vessel elements are both dead at functional maturity, meaning that they are actually dead when they carry out their job of transporting water throughout the plant body.
Sieve cells conduct sugars and other organic compounds, and are arranged end-to-end with pores called sieve plates between them to allow movement between cells. They are alive at functional maturity, but lack a nucleus, ribosomes, or other cellular structures.
Sieve cells are thus supported by companion cells, which lie adjacent to the sieve cells and provide metabolic support and regulation. The xylem and phloem always lie adjacent to each other. In stems, the xylem and the phloem form a structure called a vascular bundle; in roots, this is termed the vascular stele or vascular cylinder.
How Are Cells, Tissues & Organs Related? | Sciencing
This light micrograph shows a cross section of a squash Curcurbita maxima stem. Each teardrop-shaped vascular bundle consists of large xylem vessels toward the inside and smaller phloem cells toward the outside. Xylem cells, which transport water and nutrients from the roots to the rest of the plant, are dead at functional maturity.
Phloem cells, which transport sugars and other organic compounds from photosynthetic tissue to the rest of the plant, are living.
BBC Bitesize - GCSE Biology (Single Science) - Levels of organisation - Revision 1
The vascular bundles are encased in ground tissue and surrounded by dermal tissue. Parenchyma are the most abundant and versatile cell type in plants. They have primary cell walls which are thin and flexible, and most lack a secondary cell wall.
Parenchyma cells are totipotent, meaning they can divide and differentiate into all cell types of the plant, and are the cells responsible for rooting a cut stem. Most of the tissue in leaves is comprised of parenchyma cells, which are the sites of photosynthesis.
Leaves typically contains two types of parenchyma cells: The palisade parenchyma also called the palisade mesophyll has column-shaped, tightly packed cells. Below the palisade parenchyma are the cells of the spongy parenchyma or spongy mesophyllwhich are loosely arranged with air spaces that all gaseous exchange between the leaf and the outside atmosphere.
Both of these types of parenchyma cells contain large quantities of chloroplasts for phytosynthesis. Parenchyma can also be associated with phloem cells in vascular tissue as parenchyma rays. They are long and thin cells that retain the ability to stretch and elongate; this feature helps them provide structural support in growing regions of the shoot system.
They are highly abundant in elongating stems. Schelrenchyma cells therefore cannot stretch, and they provide important structural support in mature stems after growth has ceased.
Interestingly, schlerenchyma cells are dead at functional maturity. There are two types of sclerenchyma cells: Fibers are long, slender cells; sclereids are smaller-sized.
Sclereids give pears their gritty texture, and are also part of apple cores. We use sclerenchyma fibers to make linen and rope. A cross section of a leaf showing the phloem, xylem, sclerenchyma and collenchyma, and mesophyll. There are also some differences in how these tissues are arranged between monocots and dicots, as illustrated below: In dicot roots, the xylem and phloem of the stele are arranged alternately in an X shape, whereas in monocot roots, the vascular tissue is arranged in a ring around the pith.
Levels of organisation
In addition, monocots tend to have fibrous roots while eudicots tend to have a tap root both illustrated above. In left typical dicots, the vascular tissue forms an X shape in the center of the root. In right typical monocots, the phloem cells and the larger xylem cells form a characteristic ring around the central pith. The cross section of a dicot root has an X-shaped structure at its center. The X is made up of many xylem cells. Phloem cells fill the space between the X. A ring of cells called the pericycle surrounds the xylem and phloem.
The outer edge of the pericycle is called the endodermis. A thick layer of cortex tissue surrounds the pericycle. The cortex is enclosed in a layer of cells called the epidermis. The monocot root is similar to a dicot root, but the center of the root is filled with pith.
The phloem cells form a ring around the pith. Round clusters of xylem cells are embedded in the phloem, symmetrically arranged around the central pith.