Earth Has a Rich Diversity of Plants. Plant Structure, Nutrition, and Transport. Angiosperms: Monocots and Dicots. Angiosperms: Dicots

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1 Plant Structure, Nutrition, and Transport Earth Has a Rich Diversity of Plants There are over 280,000 different plant species organized into four major groups: bryophytes (mosses), seedless vascular plants, gymnosperms, and angiosperms Angiosperms: Monocots and Dicots Angiosperms can be divided into two main groups based on their external structure Dicots are the largest group of flowering plants with about 175,000 species Monocots include all the grasses, members of the lily family, palm trees, and banana plants Mono vs. Dicots Angiosperms: Dicots Dicots have leaf veins, which contain vascular tissues and are arranged in a netlike pattern The taproot is the main root of a dicot Dicots have two cotyledons, food storing organs that are part of the tiny, embryonic seedling that lies inside a seed Examples: roses, maples, oaks, geranium Angiosperms: Monocotes The leaf veins of monocots are arranged parallel to each other, and the plants are anchored in the ground by a tuft like mass of roots known as a fibrous root A monocot seed has a single, small cotyledon that remains belowground in the seed husk The Plant Body The body of a plant can be divided into the root system belowground and the shoot system aboveground All flowering plants have three types of organs: roots, stems, and leaves Each plant organ is made up of three main types of tissue that collectively carry out a set of related functions 1

2 Roots anchor, absorb nutrients, and store food Purpose of root hairs? The root cap is azone of active cell division protected by a conical patch of tissue at the tip of each root Plant Organ: Roots Dicots have a dominant taproot that grows directly down into the ground Plant Organ: Roots Monocots produce fibrous roots that form dense mats that help hold soil in place Aerating roots rising above the ground Adaptations in Roots Carrots are a modified tap root Stems allow plants to grow against the pull of gravity and hold up leaves to absorb sunlight The stem consists of: dermal tissue at the external surface ground tissue in the interior and bundles of vascular tissue embedded in the ground tissue Plant Organ: Stems Dicot Stem Adaptations in Stems Adaptations in Stems Iris Ginger Running Bamboo Stolon are stems that grow horizontally across the ground. Rhizomes are horizontal underground stems that send out shoots and roots. Stores carbohydrates, proteins and other nutrients 2

3 Adaptations in Stems Plant Organ: Leaves Blade Petiole Potato tubers are modified stems, weird? Sweet potato tubers are modified roots. Fleshy base of leaves Stem Broad portion of the plant to increase surface area for photosynthesis and gas exchange Blade flattened portion Petiole stalk that joins the leaf to stem Plant Organ: Leaves Stomata are regulated air pores in the dermal layer of leaves that control gas exchange (+CO 2 ) Stomata are responsible for the intake of carbon dioxide needed to carry out photosynthesis Photosynthesis takes place in the ground tissue, which also houses vascular tissues containing phloem and xylem Adaptations in Leaves Sliced leaves reduce wind resistance Hairs on the leaf surface trap humidity Waxy leaf surfaces reduce water loss. Adaptations in Leaves Petals attracts pollinators Inclusions of crystalline minerals deter herbivores Adaptations in Leaves Special leaves on carnivorous plants are adapted to trapping food Spines protect the plants Silica deposition in cell walls Tendrils allow the plant to climb Bulbs store food and water 3

4 Adaptations in Leaves Large surface area provides large area for sunlight and shade for plant to minimize heating and reduce water loss. Adaptations in Leaves and Co Evolution Succulent leaves store water Aromatic oils, poisons or pheromones produced by leaf borne glands deter herbivores Aromatic oils, poisons or pheromones produced by leaf borne glands deter herbivores Plant Tissues Dermal tissue forms the outermost layer Vascular tissues are made up of two main types of tube like cells that conduct water and food: Xylem transports water Phloem transports food Ground tissue is any other type of tissue found in plants Dermal Tissues Interact with the Environment The dermal tissue consists of a single layer of rectangular protective cells that form the epidermis A waxy cuticle covers the epidermis aboveground, which helps prevent water loss and keeps pathogens out of the plant Cuticle Dermal tissue (epidermis) Dermal Tissues Interact with the Environment The leaves, stems, and even fruits of many plants are covered with dermal hairs that protect the plant from UV rays and herbivores Root hairs play an essential role in the uptake of water and nutrients Cuticle Dermal hair Dermal tissue (epidermis) Adaptations in the Dermal Tissue of Plants Dermal hairs on the edelweiss that protects it from high UV light Dermal hairs protect many plants from insects 4

5 Ground Tissues Have Many Essential Roles Support: Pressure from water within the cells acts as a skeleton (turgor pressure) Cell walls provide mechanical reinforcement Nutrients: Photosynthesis storage of surplus food Protection: Wound repair Vascular Tissues Transport Food and Water Plants have two types of vascular tissues made up of long cells that form continuous tubes: Phloem transports food, such as sugars, from the leaves to the rest of the plant. Made of living cells. Xylem transports water and minerals absorbed from the soil to the rest of the plant. Made of dead cells. Phloem Xylem Xylem Transport Is Driven by Transpiration Xylem Transport Is Driven by Transpiration The evaporation of water from the shoot surface of a plant is known as transpiration and takes place mostly through open stomata Water coats the surfaces of cells within a leaf, which also contains many air spaces Properties of Water Is a polar molecule Polar molecules contain an uneven distribution of electrical charges that make one end of the molecule slightly negative and the other end slightly positive Hydrogen bonds form between positively charged hydrogen atoms and adjacent, negatively charged oxygen atoms The polarity of water and the resulting hydrogen bonds are what give water its unique properties Properties of Water 5

6 Hydrogen Bonding Accounts for the Cohesion of Water Molecules Properties of Water The hydrogen bonds between water molecules generate an attractive force called cohesion which creates surface tension Properties of Water Xylem Transport Is Driven by Transpiration Transpiration from leaf surfaces generates a lifting force, called surface tension, that exists at all air water boundaries This surface tension generates a curved surface in the water film at an air water boundary, causing the water film to recede into microscopic cracks in plant cell walls Stoma Xylem Transport Is Driven by Transpiration As water is lost from the water film, it becomes more curved and its surface tension becomes stronger. The surface tension that exists is transmitted to the water column in the xylem, which pulls it upward from the roots The cohesion of water molecules maintains a continuous water column in the xylem. Stoma Stomata and Transpiration The stomata can also regulate transpiration. When there is plenty of water for the plant the stomata are open When water is scares the stomata are closed This is controlled by the guard cells around the stomata. 6

7 Phloem Transport Is Driven by Osmosis Using energy the plant pumps sugar from photosynthesis into the phloem cells in the leaves Phloem Transport Is Driven by Osmosis Through osmosis water rushes into the phloem cells generating high pressure, pushing the fluid towards a lower pressure At this point the plant is using osmosis rather than energy to move the sugar. Phloem Transport Is Driven by Osmosis Cells that are respiring pull the sugar out of the phloem cells. With a decrease in the sugar concentration water leaves too creating lower pressure Photosynthesis: How Plants Obtain Energy Energy Used H 2 O + CO 2 Glucose + O 2 Plants need air, water, and the sun s energy to grow They use sunlight, CO 2, and H 2 O to make sugars that will be used by the plant cells for cellular energy How Plants Use the Energy they Make Cellular Respiration: Energy Released Glucose + O 2 H 2 O + CO 2 The sugar made during photosynthesis are broken down during cellular respiration to produce ATP, the cell s energy molecule Plants and Energy Energy Used H 2 O + CO 2 Glucose + O 2 Energy Released Glucose + O 2 H 2 O + CO 2 What do you notice about these two equations? This is how all cells get energy from the foods they eat. 7

8 Plants Need Mineral Nutrients to Grow Some of the energy obtained from Photosynthesis and cellular respiration are used to absorb nutrients. Plants require: From the soil: Macronutrients require large amounts Micronutrients require much smaller amounts From the air and water: Carbon, oxygen, and hydrogen Plant fertilizers contain the macronutrients nitrogen (N), phosphorus (P), and potassium (K) because they are typically depleted from the soil after repeated harvests Absorbing Nutrients from the Soil Mineral nutrients commonly enter the root through root hairs and travel from one cell s cytosol to another s Absorbing Nutrients from the Soil Roots also absorb nutrients by passing nutrients from one cell wall to the next The endodermis is a type of ground tissue that functions as a gatekeeper for nutrients entering the vascular tissues 8