All organisms are made of cells. There are 3 basic types of plant cells. Parenchyma cells are loosely packed, cube-shaped or long cells with a large central vacuole and thin, flexible cell walls [they hold water and are flexible]. Most of nonwoody plants are made of this. Collenchyma cells are thicker and irregular in shape. They provide support for parts of plants that are still lengthening. They are grouped in strands. Sclerenchyma cells have thick, rigid cell walls. They support parts of the plant where growth is no longer occurring.
There are 3 systems of tissues that are vital to plants. (Figure 1) Dermal Tissue System
This forms the outside of plants. It includes the epidermis (outer layer made of parenchyma cells) and the cuticle, a waxy layer that prevents water loss. Stomata are openings in the leaf and stem epidermis that regulate gasses and moisture in the plant.
Ground Tissue System
Ground tissue is used for metabolism, support, and storage. Parenchyma cells are common in this system. These cells store water, so plants like Cactus have many parenchyma cells. These are the roots and if there is a lot of water, their parenchyma cells usually have spaces between them so that air can get to the roots.
Vascular Tissue System
Ground tissue surrounds the vascular tissue system. In Angiosperms, xylem has two major components, tracheids and vessel elements. Both are dead at maturity. A tracheid is a long, thick-walled sclerenchyma cell with tapering ends. Water moves from one to another through pits, which are thin, porous holes in the cell wall. A vessel elementis a sclerenchyma cell with either large holes at the top and bottom or no walls at all. These are stacked to create hollow tubes called vessels. Tracheids are considered primitive and are present in the xylem of most seedless vascular plants and most gymnosperms. The main parenchyma cell of angiosperm phloem is called a sieve tube member. These stack to form sieve tubes. Compounds move between end walls called sieve plates to the cells next to them, called companion cells. Phloem also usually contains sclerenchyma cells called fibers. [examples: hemp, flax]
*This part right above may seem kind of difficult to understand, but on page 585 in your bio textbook, there is a really helpful diagram*
Plant growth is mainly in meristems, regions where cells keep dividing using mitosis. Apical meristems are located at the tips of stems and roots. [think, apical=tips]. Some monocots grow in length through intercalary meristems located above the bases of leaves and stems; these help things grow after being cut. Gymnosperms and most Dicots also have lateral meristems, which allow stems and roots to get thicker. There are 2 types. The vascular cambium, between the Xylem and phloem, makes additional vascular tissues. The cork cambium, outside of the phloem, makes cork. Cork replaces the epidermis in woody stems and roots. The wood prevents water loss and provides production. Growth in length is called primary growth and uses apical and intercalary meristems. Growth in height is called secondary growth and uses lateral meristems.
Figure 1
29.2 Roots
When a seed sprouts, it makes a primary root. If that root becomes the biggest, it is called a taproot. Taproots rarely go down more than a few meters, though some species, like cottonwoods, have a taproot over 150 feet to reach underground water reserves. In other plants, the primary roots does not become large. If no taproot is visible, the roots are said to be a fibrous root system. These often develop monocots. Special roots that grow from uncommon places, such as stems or leaves, are called adventitious roots. [corn has these kind of roots][See figures 1 and 2]
Root structures are the way they are for several reasons. The root cap is a layer on top of the apical meristem that makes a slimy lubricant, which helps the root penetrate the soil. Most roots form symbiotic relationships with fungi to make a mycorrhiza. Root hairs are extensions of epidermal cells that increase surface area and therefore the plants ability The hyphae of these mycorrhiza also increase surface area for more absorption. Roots are used for storage of energy as starch and getting water. They are dependent on leaves for their energy.
Roots increase in length through cell division, elongation, and maturation in the apical meristem. The cortex is located just inside the epidermis. The innermost boundary of the cortex is called the endodermis. These cells contain a waterproof layer that keeps water from spilling out through the xylem. This endodermis controls the flow of materials into the vascular tissue. In dicots, xylem usually forms and X, while in monocots, xylem occurs in many patches that circle the pith. The outermost layers is called the pericycle. Lateral roots are formed by the division of pericycle cells. Dicot and gymnosperm roots often experience secondary growth (growing thicker). The vascular cambium produces secondary xylem towards the inside and secondary phloem towards the outside of the root. This crushes everything outside the phloem, like the endodermis, cortex and epidermis. A cork cambium forms and replaces crushed cells with cork.
Roots anchor plants in soil. They absorb water, many minerals, macronutrients and micronutrients. Macronutrients, such as nitrogen and potassium, are elements required in amounts greater than 1000mg/kg of dry matter. Other minerals, like manganese, are called micronutrients and are required in amounts less than 100mg/kg dry matter. [Those numbers are read, 100 miligrams for every kilogram of dry matter in the plant] Some roots also store carohydrates, sugar, and water.
Figure 1
Figure 2, Adventitous
Figure 3
29.3 Stems
A typical stem is either woody or nonwoody. Stems show adaptations to the environment. Strawberries use stolons which grow along the ground. Cactuses have green fleshy stems that store water and do all the photosynthesis. Other stems have thorns as protection from plants. Stems, like roots, grow in length at the tips. Each leaf is attached to the stem at a node. The space between nodes is called internodes. At the point of attachement of each leaf, the stem has a bud. A bud is capable of developing into a new shoot system. A bud contains an apical meristem and is covered by bud scales. In some plants, the terminal bud at the tp and the bud scales fall off when growth resumes in the spring. These bud scales leave scars.
Apical meristems still make dermal, ground, and vascular tissues. In gymnosperm and dicot stems, ground tissue usually form a cortex and a pith. The pith is located in the center of the stem. Vascular tissue formed near the apical meristem occurs in bundles. Monocot stem vascular bundles are usually scattererd throughout the ground tissue. Stems increase in thickness with the division of cells in the vascular cambium. Secondary xylem, called wood, is produced. Older parts of the xylem stop transporting water, and fill with resin. It becomes discolored heartwood. The functional, ligghter part of the tree is called sapwood. It is usually the heartwood that thickens. During spring, the large amount of water makes wide, thin xylem, called springwood. In the summer, when there is not as much water, Xylem cells have thicker walls and are closer together, making summerwood. During winter, trees are dormant. The annual ring is the abrupt change between spring and summerwood. Annual rings don't form on tropical plants because there is constant water year-round.
Stems use sources and sinks. The source is where the material is made and the sink is where it will be stored or use. Translocation refers to the movement of sugars from the leaves to the roots. The movement of sugars in the phloem is explained by the pressure flow hypothesis. Sugars are transported by using active transport. Water osmoses into the hypertonic tubes filled with sugar and pushes them down. The transportation of water is called transpiration. According to the cohesion-tension theory, water is pulled up the stem by the strong attraction of the water molecules to each other, cohesion, and the strong attraction to the molecules of the xylem cell walls, called adhesion. Plant stems are used for storage in many species of plants, cacti being a prime example.
Pressure Flow Hypothesis
29.4 Leaves
A tendril is a modified leaf found in many vines. Leaves are often modified into spines that protect the plant from being eaten by animals. Leaves come in a wide variety of shapes and sizes. The broad, flat part of the leaf is the blade. The blade is usually attached to the stem by a stalklike petiole. Maple leaves are simple leaves, there is only one blade. In compound leaves, the blade is divided into leaflets. Leaves have many openings on their surface called stomata that regulate the flow of gasses. In omst plants, photosynthesis occurs in the leaf mesophyll, a ground tissue composed of chloroplast-rich parenchyma cells. In most plants, the mesophyll is organized into two layers. The palisade mesophyll layer occurs directly beneath the upper epidermis and is the sight of most photosynthesis. Palisade cells are columnar and appear to be packed tightly together in one or two layers. Beneath the palisade layer is the spongy mesophyll. It has irregularly shaped cells and large air spaces for oxygen, Carbon Dioxide, and water to diffuse outside the cell. Veins are the vascular system of leaves. Venation is the arrangement of veins of leaves. Most monocots have parallel venation. meaning that several main veins are roughly parallel to each other. Mos dicots have net venation, meaning that the main vein or veins branch to make a network of veins.
Alot of water is lost through transpiration, almost 98% in plants like corn. However, transpiration does cool the plant down. The leaves of some plants have adapted to maximize light interception. Leaves with lots of sun tend to be smaller and have more chloroplasts per square inch. In dry environments, plants often get more sunlight than they can use. Some plants have hairs that lower the amount of sunlight absorbed to take care of this. Plants must regulate their stomata. Guard cells, are modified cells on the leaf epidermis that regulate gas and water exchange. The stomata of most plants open during the day and close at night. Stomata also close if water is scarce.
29.1 Plant Cells and Tissues
All organisms are made of cells. There are 3 basic types of plant cells. Parenchyma cells are loosely packed, cube-shaped or long cells with a large central vacuole and thin, flexible cell walls [they hold water and are flexible]. Most of nonwoody plants are made of this. Collenchyma cells are thicker and irregular in shape. They provide support for parts of plants that are still lengthening. They are grouped in strands. Sclerenchyma cells have thick, rigid cell walls. They support parts of the plant where growth is no longer occurring.
There are 3 systems of tissues that are vital to plants. (Figure 1)
Dermal Tissue System
This forms the outside of plants. It includes the epidermis (outer layer made of parenchyma cells) and the cuticle, a waxy layer that prevents water loss. Stomata are openings in the leaf and stem epidermis that regulate gasses and moisture in the plant.
Ground Tissue System
Ground tissue is used for metabolism, support, and storage. Parenchyma cells are common in this system. These cells store water, so plants like Cactus have many parenchyma cells. These are the roots and if there is a lot of water, their parenchyma cells usually have spaces between them so that air can get to the roots.
Vascular Tissue System
Ground tissue surrounds the vascular tissue system. In Angiosperms, xylem has two major components, tracheids and vessel elements. Both are dead at maturity. A tracheid is a long, thick-walled sclerenchyma cell with tapering ends. Water moves from one to another through pits, which are thin, porous holes in the cell wall. A vessel elementis a sclerenchyma cell with either large holes at the top and bottom or no walls at all. These are stacked to create hollow tubes called vessels. Tracheids are considered primitive and are present in the xylem of most seedless vascular plants and most gymnosperms. The main parenchyma cell of angiosperm phloem is called a sieve tube member. These stack to form sieve tubes. Compounds move between end walls called sieve plates to the cells next to them, called companion cells. Phloem also usually contains sclerenchyma cells called fibers. [examples: hemp, flax]
*This part right above may seem kind of difficult to understand, but on page 585 in your bio textbook, there is a really helpful diagram*
Plant growth is mainly in meristems, regions where cells keep dividing using mitosis. Apical meristems are located at the tips of stems and roots. [think, apical=tips]. Some monocots grow in length through intercalary meristems located above the bases of leaves and stems; these help things grow after being cut. Gymnosperms and most Dicots also have lateral meristems, which allow stems and roots to get thicker. There are 2 types. The vascular cambium, between the Xylem and phloem, makes additional vascular tissues. The cork cambium, outside of the phloem, makes cork. Cork replaces the epidermis in woody stems and roots. The wood prevents water loss and provides production. Growth in length is called primary growth and uses apical and intercalary meristems. Growth in height is called secondary growth and uses lateral meristems.
29.2 Roots
When a seed sprouts, it makes a primary root. If that root becomes the biggest, it is called a taproot. Taproots rarely go down more than a few meters, though some species, like cottonwoods, have a taproot over 150 feet to reach underground water reserves. In other plants, the primary roots does not become large. If no taproot is visible, the roots are said to be a fibrous root system. These often develop monocots. Special roots that grow from uncommon places, such as stems or leaves, are called adventitious roots. [corn has these kind of roots][See figures 1 and 2]
Root structures are the way they are for several reasons. The root cap is a layer on top of the apical meristem that makes a slimy lubricant, which helps the root penetrate the soil. Most roots form symbiotic relationships with fungi to make a mycorrhiza. Root hairs are extensions of epidermal cells that increase surface area and therefore the plants ability The hyphae of these mycorrhiza also increase surface area for more absorption. Roots are used for storage of energy as starch and getting water. They are dependent on leaves for their energy.
Roots increase in length through cell division, elongation, and maturation in the apical meristem. The cortex is located just inside the epidermis. The innermost boundary of the cortex is called the endodermis. These cells contain a waterproof layer that keeps water from spilling out through the xylem. This endodermis controls the flow of materials into the vascular tissue. In dicots, xylem usually forms and X, while in monocots, xylem occurs in many patches that circle the pith. The outermost layers is called the pericycle. Lateral roots are formed by the division of pericycle cells. Dicot and gymnosperm roots often experience secondary growth (growing thicker). The vascular cambium produces secondary xylem towards the inside and secondary phloem towards the outside of the root. This crushes everything outside the phloem, like the endodermis, cortex and epidermis. A cork cambium forms and replaces crushed cells with cork.
Roots anchor plants in soil. They absorb water, many minerals, macronutrients and micronutrients. Macronutrients, such as nitrogen and potassium, are elements required in amounts greater than 1000mg/kg of dry matter. Other minerals, like manganese, are called micronutrients and are required in amounts less than 100mg/kg dry matter. [Those numbers are read, 100 miligrams for every kilogram of dry matter in the plant] Some roots also store carohydrates, sugar, and water.
29.3 Stems
A typical stem is either woody or nonwoody. Stems show adaptations to the environment. Strawberries use stolons which grow along the ground. Cactuses have green fleshy stems that store water and do all the photosynthesis. Other stems have thorns as protection from plants. Stems, like roots, grow in length at the tips. Each leaf is attached to the stem at a node. The space between nodes is called internodes. At the point of attachement of each leaf, the stem has a bud. A bud is capable of developing into a new shoot system. A bud contains an apical meristem and is covered by bud scales. In some plants, the terminal bud at the tp and the bud scales fall off when growth resumes in the spring. These bud scales leave scars.
Apical meristems still make dermal, ground, and vascular tissues. In gymnosperm and dicot stems, ground tissue usually form a cortex and a pith. The pith is located in the center of the stem. Vascular tissue formed near the apical meristem occurs in bundles. Monocot stem vascular bundles are usually scattererd throughout the ground tissue. Stems increase in thickness with the division of cells in the vascular cambium. Secondary xylem, called wood, is produced. Older parts of the xylem stop transporting water, and fill with resin. It becomes discolored heartwood. The functional, ligghter part of the tree is called sapwood. It is usually the heartwood that thickens. During spring, the large amount of water makes wide, thin xylem, called springwood. In the summer, when there is not as much water, Xylem cells have thicker walls and are closer together, making summerwood. During winter, trees are dormant. The annual ring is the abrupt change between spring and summerwood. Annual rings don't form on tropical plants because there is constant water year-round.
Stems use sources and sinks. The source is where the material is made and the sink is where it will be stored or use. Translocation refers to the movement of sugars from the leaves to the roots. The movement of sugars in the phloem is explained by the pressure flow hypothesis. Sugars are transported by using active transport. Water osmoses into the hypertonic tubes filled with sugar and pushes them down. The transportation of water is called transpiration. According to the cohesion-tension theory, water is pulled up the stem by the strong attraction of the water molecules to each other, cohesion, and the strong attraction to the molecules of the xylem cell walls, called adhesion. Plant stems are used for storage in many species of plants, cacti being a prime example.
29.4 Leaves
A tendril is a modified leaf found in many vines. Leaves are often modified into spines that protect the plant from being eaten by animals. Leaves come in a wide variety of shapes and sizes. The broad, flat part of the leaf is the blade. The blade is usually attached to the stem by a stalklike petiole. Maple leaves are simple leaves, there is only one blade. In compound leaves, the blade is divided into leaflets. Leaves have many openings on their surface called stomata that regulate the flow of gasses. In omst plants, photosynthesis occurs in the leaf mesophyll, a ground tissue composed of chloroplast-rich parenchyma cells. In most plants, the mesophyll is organized into two layers. The palisade mesophyll layer occurs directly beneath the upper epidermis and is the sight of most photosynthesis. Palisade cells are columnar and appear to be packed tightly together in one or two layers. Beneath the palisade layer is the spongy mesophyll. It has irregularly shaped cells and large air spaces for oxygen, Carbon Dioxide, and water to diffuse outside the cell. Veins are the vascular system of leaves. Venation is the arrangement of veins of leaves. Most monocots have parallel venation. meaning that several main veins are roughly parallel to each other. Mos dicots have net venation, meaning that the main vein or veins branch to make a network of veins.
Alot of water is lost through transpiration, almost 98% in plants like corn. However, transpiration does cool the plant down. The leaves of some plants have adapted to maximize light interception. Leaves with lots of sun tend to be smaller and have more chloroplasts per square inch. In dry environments, plants often get more sunlight than they can use. Some plants have hairs that lower the amount of sunlight absorbed to take care of this. Plants must regulate their stomata. Guard cells, are modified cells on the leaf epidermis that regulate gas and water exchange. The stomata of most plants open during the day and close at night. Stomata also close if water is scarce.