By the end of this lesson you will be able to:
- Label the parts of a plant cell.
- List the types of tissues in a plant and describe where they are located and the specialized cells that make up each of these tissues.
- Summarize the key functions of those tissues.
The graphic below illustrates the key parts of the plant cell.
The outer covering of the cell, the is a rigid membrane that contains cellulose (a carbohydrate that is indigestible for humans). The cell wall protects the parts inside, and the cellulose molecules in the wall provide the support and rigidity needed to maintain the cell’s three-dimensional structure.
The is made up of layers of protein and lipid (fats and oils are examples of lipids). The cell membrane is semi-permeable — it allows select compounds in and out, but blocks other types of compounds. If the cell were like a bicycle tire, the cell wall would be the thick, protective outer tire tread and the cell membrane would be the inner tube.
An (“organelle” is the generic name for a plant organ) that contains chlorophyll. In the chloroplast, light energy is captured and the first steps are taken in the chemical pathway that converts the energy in light into forms of energy that the plant can transport and store, like sugar and starch. are not evenly distributed throughout the plant but, as you might expect, are concentrated in parts of the plant that are exposed to and oriented toward the sun. A plant cell in the leaf blade will have many chloroplasts, while cells in the middle of the stem will have few or none.
(Singular = mitochondrion)
The is where stored sugars from photosynthesis are metabolized to produce forms of energy that the plant can use for growth. This metabolism is known as respiration and uses oxygen to convert sugars (and other carbohydrates) to energy and carbon dioxide. This is the cell’s power plant. All cells have numerous mitochondria.
An organelle that contains the chromosomes. Chromosomes contain the genetic material (deoxyribonucleic acid; DNA) that is carried within each cell and that directs which chemical reactions are turned on and off in the cell. Chromosomes are the hereditary material passed on to new cells and to subsequent generations. Each cell has one .
An organelle containing various fluids, ions, chemical energy, and waste products from the cell. The takes up much of the cell volume and gives shape to the cell.
The fluid inside the cell membrane in which the organelles and other plant cell parts are suspended.
A material containing pectin that forms between cells and cements the cell wall of one cell to the cell wall of an adjacent cell. If bricks in a wall are like cells in a plant, the in the plant is like the mortar between bricks in the wall.
Plant cells have other parts as well, but these are the key ones to know and understand now.
- What is the difference in function between the cell wall and the cell membrane?
- What is the mortar that holds cells together? If lettuce is grown in a soil with low calcium content, the outer edges of leaves can degenerate and die, causing tip burn. Could this involve the mortar that holds cells together?
- Where is light energy captured?
- What happens in the mitochondria, and what is the connection between that function in mitochondria and the function of chloroplasts?
A is a group of cells that share a function. The cells within a tissue may differ from one another, but they all contribute to a particular function. We’re going to look at three types of tissues: dermal, cortex, and vascular.
(derma is Greek for “skin”) are on the outside of the plant and provide protection for the plant cells they surround. The cells making up dermal tissues are tough so that they can protect against mechanical challenges to the plant, like abrasion. They have thick cell walls. In the shoot, the cells, which are the main cell type in dermal tissue, secrete a water-resistant substance called cutin (a waxy polymer), which coats the wall of the cell exposed to the environment. This coating helps limit the loss to the atmosphere of water that is inside the plant. Cutin is absent or greatly reduced in root tissue because roots need to reach out into the soil to absorb water and nutrients.
The epidermis is the outermost layer of cells in the plant. It is normally only one cell thick, but in some cases the epidermis can be a few cells thick. Epidermis cells typically have few if any chloroplasts. They are often called pavement cells because they are flat like tiles or puzzle pieces. Depending on the plant, the epidermis may have hairs, or trichomes, that extend out from the plant. Some of these trichomes are associated with glands that contain oils or other substances secreted by the plant.
The epidermis contains pairs of guard cells that will open to form stomata (Greek stoma = mouth; an opening in the leaf surface) through which gasses can move into and out of the deeper cell layers in the leaf. These guard cells are found most abundantly on the underside of leaves, but may also be on the upper leaf surface and on the stems.
The root has dermal tissue as well. The predominant cell type, like in the shoot, is also epidermis, but as noted above there is no cutin covering the root epidermis because the root is underground and less prone to dehydration. There are no guard cells or trichomes, but there are root hairs . The root hair is a very small-diameter extension of the epidermis cell wall and cell membrane that extends out into the growth medium. Water and nutrients enter the plant through absorption into the root hairs.
- What unique feature of the epidermis is found in roots and not shoots?
- What is the function of the waxy cutin layer? Why don’t you find it on the root epidermis?
- Are stomata found in roots, shoots, or both? Why does this make sense?
- What’s the difference between a cell and a tissue?
Cortex or ground meristem tissue
The cortex (sometimes called ““) tissue is found just inside the epidermis and extends toward the interior of the stem and root. Some types of plants also contain cortex tissue at the very center of the stem called the pith, but you won’t find pith in roots or in all plant stems. Cortex cells provide structural support for the stems. In leaves, this tissue just inside the epidermis is called the (“middle of the leaf”). Mesophyll tissue is the site of most photosynthesis reactions in the leaf.
Three types of cells make up the cortex:
- The most common type of cortex cell.
- Has thin cell walls (called a primary wall in the graphic below).
- The mature cell is alive.
- Has the ability to begin dividing to help heal wounds (by covering the wound with plant tissue called ).
- Will also divide to initiate adventitious roots on stem cuttings.
- Site of many other functions, such as photosynthesis and storage of starch and other chemical compounds.
- Leaf mesophyll tissue is a type of that is packed with chloroplasts.
- A living cell at maturity.
- Cell walls are thicker than the thin parenchyma cell walls, which give strength. However, these cells remain somewhat flexible compared to , which you will read about next.
- The cells can connect together to form resilient strands, like the strands of a celery stalk. These strands provide support for young tissues.
- Because the cells are alive, they can respond to external stimuli. If the plant is regularly shaken by wind, for example, the collenchyma cells will respond by producing thicker cell walls for greater support of the plant stem so that it can remain upright.
- This type of cell has a primary and secondary cell wall. The primary cell wall, on the outside of the cell, is rich in cellulose, just like other plant cell walls. Once the cell has reached its final size, a secondary cell wall is deposited just inside the primary wall. The secondary wall has a high concentration of lignin that gives the cell rigidity. This rigid, lignified secondary cell wall is responsible for sclerenchyma’s hardness and strengthening properties. Sclerenchyma comes in two types:
- Fibers (see below) formed from long strands of sclerenchyma. These tough fibers give the plant rigidity. We extract these fibers from plants and use them in fabrics, carpets, and rope. Examples of plant fibers made up of sclerenchyma cells include jute, hemp, and flax (the fabric made of flax fibers is called linen). Cotton is not in this list; it is an epidermal fiber produced by the plant’s seed coats.
- Sclereids are cells with hard, tough cell walls. Sclereid cells can coalesce and cover other plant parts. For instance, they form the hard covering around the seeds (the endocarp) of stone fruits like cherries, the hard shell around walnuts, and the hard covering of coconut. Sclereids also make up the grit that crunches between your teeth when you eat a pear.
- Sclerenchyma cells are dead at maturity. They don’t thicken in response to external stimuli the way collenchyma can.
- Which cortex cells are alive and which are dead when mature?
- Which cells make up the tough fibers from which rope and fabrics can be made?
- Which cells divide to initiate adventitious roots?
- What tissue in the leaf corresponds to the cortex in the stem?
Vascular tissues form the plumbing system in the plant through which water, nutrients, sugars, and other compounds flow. These plumbing pipes and associated cells are bundled together in the plant in a structure called the vascular bundle. There are three main types of vascular tissue: xylem, phloem, and vascular cambium. Xylem and phloem are composed of different types of cells, listed below.
- Moves water in the plant.
- The water flow is unidirectional. Water in xylem heads from root to stem to leaf and then out of the plant stomates through a process called transpiration.
- The part of the tree that we call “wood” is made up of xylem.
- These cells are dead at maturity, and they are hollow.
Xylem tissue is composed of four different types of cells:
Elongated cells that connect end to end to form tubes. The cells are dead at maturity. The end walls of the are perforated, so water can move freely through the holes and flow from cell to cell. Vessels have a relatively large diameter compared to other xylem cells and allow greater movement of water.
These cells are elongated and narrower than vessels, and connect by overlapping at their ends. These cells are also dead at maturity and contain pits through which water can move. appear earlier in the paleontological record of plant evolutionary development than vessels and are thus considered “primitive” (not inferior, but appearing earlier in evolutionary time). Vessels are a subsequent evolutionary adaptation that allow for greater water flow because of their larger diameter.
Sclerenchyma cells lying near the vessels and tracheids, and thus part of the vascular bundle. They are strung together end to end like the vessels and tracheids, but unlike those water carriers they have no pits or perforations and instead have thick primary and secondary cell walls. They provide flexible support for the plant from within the vascular bundles.
In woody plants there are parenchyma cells around the vascular bundles that extend horizontally through the xylem (the woody part of the plant) and develop into rays moving laterally from the center to the exterior of the plant. Most of the vascular cell types are arranged in a linear fashion parallel to the long axis of the stem, but parenchyma rays are arranged laterally from the middle of the stem out toward the epidermis. They function to conduct water through the wood (xylem). Oak furniture for example, it will have a “grain” which is caused by the annual rings of xylem, and will have rays that, on edge, look like small pits in the wood. We will see this in later lectures when we deal more extensively with wood and secondary growth. As you can see in the photo to the right, some of the natural markings you see in an instrument’s wood are from parenchyma rays.
- Moves some nutrients taken up by the roots to other parts of the plant.
- Moves sugars manufactured in leaves by photosynthesis, and other plant compounds such as plant hormones like auxin, to other parts of the plant.
- The flow in the phloem is multi-directional among leaf, stem, and root.
Phloem tissue also has four types of cells:
Sieve tube members
Elongated cells that join end to end to form tubes for passage of liquids. The end walls have pores. Unlike xylem cells, these cells are still alive. They have a thin cell membrane containing a layer of living protoplasm that hugs the wall of the cell.
Associated with . Contain a nucleus, may direct the metabolism of the sieve tube member, and are alive.
Phloem fibers (sclerenchyma cells)
Provide support, same as for xylem.
Phloem parenchyma cells
Adjoin the sieve tube cells, same as for xylem.
This third type of vascular tissue is a meristematic region (meaning that the cells can actively divide to form new growth) where new vascular tissues originate in plants with secondary growth, like trees. We will study secondary growth in Chapter 6.2.
- What substance flows in the xylem? Does it flow both directions or only up from the roots to the leaves?
- What are examples of substances that flow in the phloem? Do these flow both directions or only from roots to leaves?
- Which vascular cells are dead and which are alive at maturity?
- Look at a piece of wooden furniture near where you are sitting. What type of plant tissue and cell do you see? Look at the natural markings in the wood. What are those tissues and cells?
The cells group together into tissues, which in plants can be simple (one type of cell) or complex (more than one type of cell). Simple plant tissues are parenchyma, collenchyma and sclerenchyma. Parenchyma cells are the least specialized type of plant cell and the most abundant in plants.What are the tissues and cells of plants? ›
The cells group together into tissues, which in plants can be simple (one type of cell) or complex (more than one type of cell). Simple plant tissues are parenchyma, collenchyma and sclerenchyma. Parenchyma cells are the least specialized type of plant cell and the most abundant in plants.How do tissues and cells function together in plants? ›
Plant tissues are composed of cells that are similar and perform a specific function. Together, tissue types combine to form organs. Each organ itself is also specific for a particular function. Plant tissue systems fall into one of two general types: meristematic tissue, and permanent (or non-meristematic) tissue.What are the names of 6 plant tissues? ›
Different plant tissues: (1) pith, (2) protoxylem, (3) xylem, (4) phloem, (5) sclerenchyma, (6) cortex, and (7) epidermis.What is plant tissue in science? ›
Plant tissue is a group of cells having a common origin and usually performing a common function in a plant body. Every plant tissue has a distinctive function and can be united with different tissues to form organs like roots, stalks, leaves, and flowers.What are 3 types of plant tissue? ›
Seeded plants have three organs: roots, stems, and leaves, and three tissue types: ground tissue, vascular tissue, and dermal tissue. Each organ include all three tissue types.What are plant cell types? ›
Plant Cell Types
The specialised plant cells include parenchyma cells, sclerenchyma cells, collenchyma cells, xylem cells and phloem cells.
Your body is made of cells and when groups of cells do the same kind of work, they are called tissues. You have four main types of tissues: Connective, Epithelial, Muscle, and Nervous tissue. Connective tissue joins bones and cushions organs.What is the main function of plant tissue? ›
Functions of plant tissues
Help provide mechanical strength to organs. They help in providing the elasticity and flexibility to the organs. They divide to produce new cells and help in the growth of the plants. They help in various cellular metabolisms like photosynthesis, regeneration, respiration, etc.
Cells make up tissues, tissues make up organs, and organs make up organ systems. The function of an organ system depends on the integrated activity of its organs.
Meristematic cells divide asymmetrically. This means that one plant remains undifferentiated, while the other cell takes on a more specialized form. This cell will then continue to divide and develop into a plant tissue, which can help form a new organ, such as a leaf.What are plant tissues called? ›
Three major types of plant tissues are dermal, ground, and vascular tissues.What is a plant tissue example? ›
Dermal tissue, for example, is a simple tissue that covers the outer surface of the plant and controls gas exchange. Vascular tissue is an example of a complex tissue, and is made of two specialized conducting tissues: xylem and phloem.What are the 4 types of tissue? ›
There are 4 basic types of tissue: connective tissue, epithelial tissue, muscle tissue, and nervous tissue.What is tissue made of? ›
Tissue is a group of cells that have similar structure and that function together as a unit. A nonliving material, called the intercellular matrix, fills the spaces between the cells. This may be abundant in some tissues and minimal in others.What are the types of cells and tissues? ›
THE 4 TYPES OF BODY TISSUE
Your body is made of cells and when groups of cells do the same kind of work, they are called tissues. You have four main types of tissues: Connective, Epithelial, Muscle, and Nervous tissue. Connective tissue joins bones and cushions organs. Epithelial tissue covers the outside of the body.
Cells are the smallest structural and functional units of an organism, which are characteristically microscopic. Tissues are clusters of cells, specialized cells. Found in both unicellular and multicellular organisms. Found only in multicellular organisms.How many cells are in plant tissue? ›
Flexi Says: Plants are multicellular organisms. The number of cells in a plant varies by species, which range from simple mosses to giant redwood trees. Large plants like trees contain trillions of cells.What are the tissues in plants with function? ›
Answer: Xylem and phloem are the conducting tissues of the vascular strands. Their main role is in the transportation of food, minerals, and water. Xylem is the tissue which is responsible for the transport of water in plants while the phloem is responsible for the transfer of food and nutrients in the plant.