Plant Biology Flashcards

25.1 Intro to Algae and Land Plants

• Objectives:
  • Describe the adaptations that allowed plants to colonize land.
  • Describe the traits shared by green algae and land plants.
  • Discuss the challenges faced by land plants.
• Algae are close relatives of plants.
  • Usually unicellular or live in colonies, but some are multicellular.
  • Plants are multicellular.
  • Require moist environments.
  • Contain photosynthetic pigments.
• Some algae look very similar to plants.
  • Chara is called muskgrass or skunkweed because of foul smell.
  • Large cells form thallus (body); branches rising from nodes are made of smaller cells.
  • Looks like some land plants, but stem has no supportive tissue.
• Life on land poses unique challenges but offers several advantages.
  • Water critical for life and provides support through buoyancy.
  • Plants need structural support on land.
  • Exposed to mutagenic radiation- more UV than in water.
  • Gamete movement impacted by dry conditions.
  • Sunlight and CO_2 more abundant on land and no predators.
• Plants used varying strategies to adapt to life on land.
  • Early land plants lived close to water.
  • Mosses dry out but revive (tolerance).
  • Colonize environments with high humidity (ferns).
  • Resistance to desiccation-gradually move further away from water.
• Plants used varying strategies to adapt to life on land.
  • Waxy cuticle resistant to desiccation (absent from some mosses).
  • Cell walls support structures off the ground.
• Apical meristems are regions of cell division giving rise to shoots and roots.
  • Shoots and roots increase in length through rapid cell division in apical meristem.
  • Think of these as plant stem cells.
  • Gives rise to all specialized tissues.
  • Elongation of shoots and roots allows access to additional space and resources (i.e., light for the shoot, water and minerals for the roots).
• Some land plants have vascular tissue.
  • Vascular tissue helps move water and nutrients.
    • Xylem-long-distance transport of water
    • Phloem-transport of sugars, proteins, and other solutes
  • Tissues extend into root-takes up water and minerals from soil and provides anchor.
• Some land plants develop defense mechanisms against predators.
  • Apparency-plants grow away from predators.
  • Structural defenses- thorns/spines.
  • Chemical defenses- compounds that result in an unappealing smell or taste.
  • Can cause severe disease and death- Sorghum produces the cyanoglycoside dhurrin.
• Summary
  • Plants and algae look similar.
  • Land plants developed tools to combat desiccation, gravity, and predation.
  • Land plants live in a range of habitats from very moist to arid.

25.2 Bryophytes: Seedless, Non-Vascular Plants

• Objectives
  • Understand the key adaptations of non-vascular land plants.
  • Describe the distinguishing traits of liverworts, hornworts, and mosses.
• Bryophytes include liverworts, hornworts, and mosses.
  • First appeared ~470 MYA
  • Lack lignin (structural polymer that makes plants woody or rigid).
  • Include over 25,000 species.
  • Require moist habitats because they lack vascular tissue.
  • Gametophyte (haploid) dominate life cycle
• Liverworts are the most primitive group of nonvascular plants.
  • ~7,000 species
  • Gametophyte dominant
  • No leaves or stomata
  • Thallus takes up water
  • Flagellated gametes
  • Can reproduce asexually by leaf fragments called gemmae
• Hornworts have stomata
  • Gametophyte dominant life cycle
  • Tall slender sporophytes emerge from parent gametophyte
  • Flagellated sperm require water for fertilization
• Mosses have a primitive conductive system
  • ~12,000 species
  • Tundra to tropical rainforest
  • Gametophyte dominant life cycle
  • Sporophyte generation has stomata
  • Primitive conductive system carries water and nutrient through gametophyte stalks
  • Anchored by rhizoids but lack true roots
  • Flagellated sperm
• Summary Seedless nonvascular plants:
  • Small
  • Gametophyte as dominant stage in life cycle
  • No vascular system or roots; absorb water and nutrients on exposed surfaces
  • Known as bryophytes
  • Include liverworts, hornworts, and mosses
  • Liverworts: Most primitive and closely related to first land plants
  • Hornworts: Developed stomata
  • Mosses: Have conductive cells and attach to substrate by rhizoids; colonize harsh habitats and regain moisture after drying out

25.3 Seedless Vascular Plants: Ferns and Their Relatives

• Objectives:
  • Understand how vascular tissue expands land plant habitats.
• Seedless vascular plants include ferns and their relatives.
  • Vascular plants emerge ~420 MYA
  • Less dependent on proximity to water
  • Sporophyte dominant life cycle
  • Still rely on damp habitats- maintain flagellated sperm
  • True leaves and roots
• Lycophyta is the earliest group of seedless vascular plants
  • ~1,200 species
  • club mosses (Lycopodiales), quillworts (Isoetales), and spike mosses (Selaginellales)
  • Does not include true mosses or bryophytes
  • Sporophyte dominant life cycle
• Equisetopsida (Horsetails) are characterized by nodes
  • Leaves and branches come out as whorls from joints
  • Needle-shaped leaves do not do much photosynthesis; instead, most photosynthesis takes place in green stem
• Psilotopsida (Whisk Ferns) have no roots or leaves
  • Photosynthesis in stems, which branch dichotomously (split into two parts)
  • Small, yellow knobs form at tip of branch or branch node and contain sporangia
• Polypodiopsida (True Ferns) have large fronds
  • More than 20,000 species live from tropics to temperate forests
  • Some can survive in dry environments, but most restricted to moist, shaded places
  • Sporophyte dominant life cycle
  • Rely on water for fertilization (flagellated sperm)

26.1-26.4 Seed plants

• Objectives
  • Discuss the purpose of pollen grains and seeds.
  • Compare and contrast angiosperms and gymnosperms
  • Understand the relationship between flowers and sexual reproduction
  • Describe how fruit aids seed dispersal
  • Distinguish monocots from dicots
• Seed plants rely less on proximity to water
  • Emerged ~350 MYA
  • Includes gymnosperms and angiosperms
  • Seed: structure containing the embryo, storage tissue, and protective coat
  • Resists desiccation
  • Dormant until conditions become favorable
  • Carried by wind, water, or animals
• Pollen reduces reliance on water for fertilization
  • Male gametophytes
  • Contain just a few cells
  • Distributed by wind, water, or animal pollinator
  • Protected from desiccation and can reach female organs without depending on water
  • After reaching female gametophyte, grows into pollen tube
    • Pollen tube: extension from the pollen grain that delivers sperm to the egg cell
• Gymnosperms have “naked seeds”
  • Four main phyla:
    • Coniferophyta
    • Cycadophyta
    • Ginkgophyta
    • Gnetophyta
  • Separate female and male gametophytes
    • Pollen cones and ovulate cones
  • Pollination by wind and insects
  • Naked seeds
  • Not enclosed in ovary
• Conifers are the dominate phylum of gymnosperms
  • Great variety of cold/drought tolerant species
  • Tall trees, scalelike or needlelike leaves, thick cuticle
• Cycads grow in tropical climates
  • Thrive in mild climates
  • Often mistaken for palms because of shape of large, compound leaves
  • Bear large strobili or cones
• Ginkgophytes have one living species
  • Ginkgo biloba only living species
  • Leaves turn yellow in autumn and fall off
  • Male and female organs on separate plants
  • Gardeners only plant male trees; female plant has off- putting smell of rancid butter
• Gnetophytes resemble angiosperms
  • Gnetophyte: gymnosperm shrub that includes the genera Ephedra, Gnetum, and Welwitschia
  • Have broad leaves like angiosperms
• Angiosperms have flowers and fruits
  • ~300,000 species
  • Sporophyte dominant life cycle
  • Flowers aid in reproduction by attracting pollinators
  • Fruits aid seed dispersal
• Fruits derived from multiple tissues
  • Two categories: Fleshy or dry
    • Fleshy: Berries, peaches, apples, grapes, tomatoes
    • Dry: Rice, wheat, nuts
  • Not all fruits derived from ovary
    • Strawberries-100-400 pistils per flower + receptacle (enlarged end of stalk or stem where flower is attached)
    • Pineapple-formed from clusters of flowers
• Fruits aid seed dispersal via multiple mechanisms
  • Variety of shapes and characteristics reflect mode of dispersal
  • Wind carries light, dry fruits of trees and dandelions
  • Water transports floating coconuts
  • Some attract herbivores with color or scent as food
  • Once eaten, tough, undigested seeds disperse through feces
• Monocots are angiosperms
  • Monocot-one cotyledon
  • Veins run parallel to and along length of leaves
  • Flower parts arranged in threes
  • True woody tissue rarely found in monocots
  • Includes true lilies (Liliopsida), orchids, yucca, asparagus, grasses, palms, rice and other cereals, corn, sugar cane, tropical fruits (e.g., bananas and pineapples)
• Dicots are angiosperms
  • Dicots- two cotyledons
  • Veins form network in leaves
  • Flower parts come in four, five, or many whorls
  • Vascular tissue forms ring in stem
  • Apples, mango, peanuts, oranges, magnolias
• Summary
  • Seeds protect embryo and provide nutrients to support early growth of sporophyte
    • Allows delayed germination until optimal conditions
  • Pollen enables reproduction without water
  • Gametophytes shrank, while sporophytes became prominent
  • Diploid stage longest phase of life cycle
  • Gymnosperms have naked seeds and pollen dispersed by wind
  • Angiosperms bear flowers and fruit.
    • Flowers expand possibilities for pollination (especially by insects, which coevolved with them).
    • Fruit offer additional protection to embryo during development and assist with seed dispersal