Chapter 17: Plant Structure and Nutrient Support How plants function and why we need them Lecture by Danielle DuCharme, Waubonsee Community College

Learning Objectives  Understand and be able to explain the following: the three basic tissue types that give rise to diverse plant characteristics. the common structural features shared by most plants.

Learning Objectives  Understand and be able to explain the following: how plants obtain sunlight and usable chemical elements to obtain nutrition from their environment. how plants transport water, sugar, and minerals through vascular tissue.

17.1 Older, taller, bigger: Plants are extremely diverse. Plants can be “superior” to animals in a variety of ways: longevity height weight energy acquisition

Extraordinary Attributes of Plants

Plants Have Three Distinct Parts The three distinct parts of plants are the: 1)roots 2)stems 3)leaves

Root System The roots serve several important functions, including absorbing water and minerals, as well as some oxygen, from the soil and anchoring plants in place.

The Shoot: Stems  Stems provide structural support for the leaves.  Stems have vascular tissue, which conducts food, water, and mineral nutrients throughout the plant.

The Shoot: Leaves  Leaves are the chief sites of photosynthesis in plants, becoming the plant’s primary food factory.  Leaves also are vulnerable to water loss through evaporation.

Take-home message 17.1  Plants are an extremely diverse and successful group of organisms, generally composed of three distinct parts: roots, stems, and leaves.

17.2 Flowering plants are divided into two major groups.  The flowering plants are classified into two major groups: monocots and dicots.  These names derive from a structure called the cotyledon.

Monocots and Dicots  Plants in which one cotyledon forms are called monocots, and plants in which two cotyledons form are called dicots.  Plants are also divided into these groups by different features in their seeds, leaves stems, flowers, and roots.

Monocots Monocots generally have: parallel veins in their leaves. vascular tissue in bundles. flower parts in multiples of three. many fibrous roots

Dicots Dicots generally have: leaves with branching veins vascular tissue arranged in an orderly ring flower parts in fours in fives a taproot

Monocots vs. Dicots

Monocot Examples  palm trees  orchids  lilies  most of the grains used in food products  all of the grasses

Dicot Examples  most plants that we consider flowers  coffee  potatoes  most fruits and vegetables  most large trees

Take-home message 17.2  The flowering plants are divided into two major groups—the monocots and the dicots—based on structural features of their seeds, leaves, stems, flowers and roots.

17.3 Plant cells and tissues differ from animal cells and tissues. There are three main tissue types in plants: 1)dermal tissue 2)vascular tissue 3)ground tissue

Dermal Tissue  Dermal tissue covers and protects the entire plant.  Dermal tissue includes a thin epidermis, a waxy cuticle, and specialized guard and cork cells.

Vascular Tissue  Vascular tissue is a system for getting nutrients to, and removing waste products from, all parts of the plant.  Sap is moved in tissue called xylem and phloem.

Ground Tissue  Ground tissue comprises most of the plant body.  Three types of cells—parenchyma, collenchyma, and sclerenchyma—are found in ground tissue.

Take-home message 17.3  All vascular plants are organized around the same basic body plan and built from the same three types of tissue.  Dermal tissue covers and protects the surface of the plant.

Take-home message 17.3  Vascular tissue transports water, sugars, and minerals throughout the plant body.  And, ground tissue, which makes up the bulk of the plant, is where most of the plant’s metabolic activities are carried out.

17.4 Roots anchor the plant and take up water and minerals.  Roots are essential to plant growth and survival.  They perform three primary functions: 1)absorption 2)anchorage 3)storage

There Are Two Types of Root Structure: Taproots and Fibrous Roots

Organization of Tissue within the Root Is Simple

Spaces Exist between Root Cells Spaces in root cells allow for gas exchange.

Take-home message 17.4  Roots have three primary functions in plants: 1)Absorption: the uptake of water and dissolved minerals from soil. 2)Anchorage: securing the plant in place. 3)Storage: for water and excess starch for future use.

17.5 Stems are the backbone of the plant. Stems provide structural support and house the circulatory system of the plant.

Stem Structure Is More Complex  Growth in stems occurs in meristems (including apical and lateral meristem) and at nodes.  Remember, dicot and monocot stems differ.

There Are Variations in Stem Structure

Take-home message 17.5  Stems serve three chief functions in plants: 1)They put leaves in positions where they can intercept sunlight and carry out photosynthesis. 2)They provide structural support for the plant. 3)They contain the xylem and phloem, through which water, minerals, and sugars are distributed throughout the plant body.

17.6 Leaves feed the plant.  The job of the leaves is to produce food for the plant.  Leaves convert the potential energy from the sun into usable chemical energy in sugars.  Plants don’t need to move to get energy— energy comes to them!

The leaf has five layers: 1)Waxy cuticle 2)Layer of non- photosynthetic cells 3)Photosynthetic cells 4)Xylem and phloem 5)Non-photosynthetic cells, with “breathing” holes called stomata. Leaves Have a Layered Structure

There Are Many Variations in Leaf Structure

The Largest Leaves and the Smallest Leaves  Water lily leaves are amongst the biggest leaves, with individual leaves measuring seven feet across!  Duckweed leaves, on the other hand, are tiny—you need 25 end to end just to measure one inch in length!

Take-home message 17.6  Leaves are thin and have a three-layer structure that enables them to effectively capture energy and transport water and nutrients.

Take-home message 17.6  Leaves intercept sunlight, putting chloroplast-containing photosynthetic cells in the path of that light and converting the potential energy of the sun into the usable chemical energy of sugar.

Take-home message 17.6  Leaves also have vascular tissue through which food is transported out of the leaf to the rest of the plant, and water and minerals are transported into the leaf.

Take-home message 17.6  Leaves also have vascular tissue through which food is transported out of the leaf to the rest of the plant, and water and minerals are transported into the leaf.

17.7 Several structures help plants resist water loss.  Water loss by evaporation is damaging to the plant.  Structures such as the waxy cuticle, surface leaf hairs, and holes called stomata resist against water loss.

These Features Help Reduce Evaporation

Take-home message 17.7  Plants have multiple adaptations that enable them to resist becoming dangerously dehydrated.  These adaptations include the cuticle, leaf hairs, and stomata.

17.8 What are the elements of plant nutrition? Plants require four things for proper nutrition: 1)Sunlight for the energy to build molecules of sugar 2)Water 3)Air as a source of carbon dioxide 4)(Usually) soil

Minerals and Essential Nutrients  There are thirteen different minerals that plants require for proper survival and growth.  Six of these essential nutrients are required in large amounts. These are: nitrogen, phosphorus, magnesium, potassium, sulfur, calcium.

Essential Plant Components

Take-home message 17.8  Plant growth is dependent on four important factors: 1)Sunlight for energy 2)Water 3)Air as a source of carbon dioxide 4)Minerals, usually obtained from soil

17.9 Nutrients cycle from soil to organisms and back again. Soil is made of four distinct components: 1)Minerals 2)Organic materials 3)Air 4)Water

Minerals  About half of the total volume of dirt is inorganic material.  These come from the weathering of rocks.  These particles come in three sizes: sand, silt, and clay.

Organic Materials  Decomposition of dead animal and plant material (humus) returns nutrients to the soil.  Decomposition is performed by bacteria, fungus, insects, and earthworms.

Composting Composting is decomposition of organic matter that can decrease the amount of waste on the planet and speed organic breakdown.

Water and Air Water and air fill the spaces between the particles of inorganic and organic matter and account for about half of the total volume of soil.

Take-home message 17.9  Soil is a mixture of minerals, organic materials, air, and water, which serves as an almost perpetual source of nutrients critical to a plant’s health and survival.

17.10 Plants acquire essential nitrogen with the help of bacteria.  Nitrogen is abundant in the atmosphere, but is a factor that can limit plant growth.  Nitrogen is used for protein construction, and that is why it is added to fertilizers.

Nitrogen Fixation  Nitrogen gas in the air must be converted to nitrate or ammonium in soil by bacteria for it to be used by plants.  This is called nitrogen fixation.

How do bacteria and plants form this mutualistic alliance?

Some Plants Have Alternative Ways of Obtaining Nitrogen  These plants ingest animals, such as insects, to obtain nitrogen they do not get in the soil, and are called carnivorous (insectivorous) plants.  One example is the Venus flytrap.

Crop Rotation To keep the soil rich in nitrogen, farmers should plant those plants that have nitrogen-fixing bacteria (i.e., alfalfa) in a rotation with those that do not (that deplete the nitrogen in the soil).

Take-home message  Among the minerals, nitrogen is the one that most commonly limits plant growth because it is required in nearly all the cells and tissues produced by plants, but does not exist in an easily usable form in nature.

Take-home message  A mutually beneficial relationship has evolved that enables plants to gain access to nitrogen that is “fixed”—that is, chemically modified into a usable form— by bacteria.

17.11 How do plants take up water and minerals? Water is transported into the root by osmosis.

Mineral Uptake Differs from Water Uptake  Minerals are chemically charged.  Therefore, active or facilitated mineral transport into the plants must be aided by transport proteins.

Plants Again Benefit from a Mutualistic Relationship  Fungi living around and within the roots increase absorptive surface area.  In exchange for providing increased vitamins and minerals to the plant, the fungus receives sugars, amino acids, and vitamins in return.

Take-home message  Plants absorb water from the soil through osmosis occurring in their root hairs.  Absorption of minerals also occurs in the roots, but this requires the help of transport proteins in root cell membranes.

Take-home message  In a mutualistic association called mycorrhizae, fungi growing into and around plant roots increase the water and mineral absorption for the plant, while gaining access to energy and nutrients from the plant.

17.12 Water and minerals are distributed through the xylem.  Evaporation is relentless.  Liquid water is continually converted to water vapor in the dry air.  This evaporation steals necessary moisture from leaves.

How is water moved through a plant?

Cohesion-Tension Mechanism In the cohesion-tension mechanism, the plant does not need to expend any energy to pump water and minerals up from the roots to the leaves.

Drawback This system of water transport limits the size to which the tree can effectively grow.

Xylem Stores Sugar to Nourish New Leaf Buds

Human Use of Sap  Humans have concentrated the sugars in sap to enjoy as a food source.  Maple syrup is created in this process.

Take-home message  Xylem directs the flow of water and dissolved minerals from the roots to all the tissues in the plant.

Take-home message  The force driving this flow of fluid (the xylem sap) comes from evaporation of water from the leaves, which pulls water up from the roots.

17.13 Sugar and other nutrients are distributed through the phloem.  Phloem is a food delivery system.  Sugar is produced in the leaves (the “source”) and transported to places (“sinks”) where sugars are needed.

Pressure-Flow Mechanism  The phloem “pipeline” moves the sugar produced in the leaves to roots, stems, buds, flowers, and fruits.  This process is the pressure-flow mechanism.

Sugar Movement Through the Plant

Organisms Besides the Plant Benefit from the Sugary Phloem Aphids pierce the plant stem to gain access to the sugary phloem.

Take-home message  The phloem consists of a branching network of vessels made from living cells lined end to end to form sieve tubes, with small openings in their side walls.

Take-home message  Sugar, usually sucrose, is moved in the phloem from sites of production (sources) to sites of use or storage (sinks).

Take-home message  The direction of flow is not always the same: a plant part may be a source at one time, and a sink at another.