chapter 10: plant reproduction, growth, and development

Chapter 10: Plant Reproduction, Growth, and Development

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Control of Plant Growth and Development

• Since each plant cell is totipotent, hormones have a role in determining cellular differentiation.

• Plant Hormones• There are five common groups of plant

hormones: auxins, gibberellins, cytokinins, abscisic acid, and ethylene.

Effects of ethylene

Positive phototropism

Negative gravitropism

Root nodules

Mycorrhizae

Chapter 8: Photosynthesis

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Radiant Energy

• Photosynthesis converts solar energy into the chemical energy of a carbohydrate in this way:

• Solar energy + carbon dioxide + water → carbohydrate + oxygen

• Photosynthetic organisms include plants, algae, and certain bacteria.

• These organisms are called producers; they synthesize organic molecules from raw materials.

Structure and Function of Chloroplasts

• Chloroplasts are the cellular organelles that carry on photosynthesis.

• Pores called stomata allow CO2 and O2 to enter the leaf.

Structure of Chloroplasts• The inner membrane encloses a large central space

called the stroma that houses enzymes used to reduce CO2 to carbohydrate.

• A membranous system of thylakoids (discs) lie within the stroma; stacked thylakoids are called: grana. Thylakoids contain chlorophyll and other pigments to capture light energy for photosynth!

• Chlorophyll and other pigments absorb solar energy which will energize electrons prior to reduction of CO2 in the stroma.

Chloroplast structureCO2 “breathed-in” throughstomata!

Solar energy + 6CO2 + 6H2O → C6H12O6 + 6O2

The light-dependent reactions: the cyclic electron pathway

The light-dependent reactions: the noncyclic electron pathway

ATP Production• Each time water is split, two H+ remain in

the thylakoid space.• As electrons move down the electron

transport system, they give up energy, which is used to pump H+ from the stroma into the thylakoid space.

• Thus, H+ build up in the thylakoid space.• The flow of H+ through an ATP synthase

complex back into the stroma drives the chemiosmotic production of ATP.

Electron transport system

The Calvin cycle (simplified)

Photosynthesis Versus Cellular Respiration

• Both plant and animal cells carry on cellular respiration in mitochondria; photosynthesis occurs in plant chloroplasts.

• Photosynthesis is the building up of glucose, while cellular respiration is the breaking down of glucose.

• Both processes occur in plant cells during daylight, but only cellular respiration occurs in plant cells at night.

Photosynthesis versus cellular respiration

EXERCISE 14: Angiosperm Leaf

Dr. L Humphrieslhumphries@elcamino.edu

Spring 2005: Fundamentals of BiologySection 1107 Biology 10 4-Units

Organization of Leaves

• Leaves are the organs of photosynthesis in vascular plants.

• Leaves have a flattened blade, that may be single or composed of leaflets, attached to a petiole.

• The epidermal layers may bear protective hairs or glands that produce irritating substances; a waxy cuticle reduces water loss and permits gas exchange.

Leaf structure

• Leaves are adapted to environmental conditions and may be broad and wide or reduced with sunken stomata.

• The leaves of a cactus are spines attached to a succulent stem.

• Climbing leaves, such as those of peas, are modified into tendrils.

• The leaves of a few plants are specialized for catching insects.

Leaf diversity

Spines(modified leaves)

Stem(photosynthetic

and storage)Angiosperm

(fruit/flowering)

Saguaro(the largest cacti

in the US- 30 ft. tall, 200 yrs. old!)

Moss(plantae)

Green Algae(plantae)

Lichen(fungi)

Human(animalia)

Gymnosperm(modified leaves!)

Gymnosperm(modified leaves!)

Gymnosperm(How is this tree

still alive?!?!)

Classification of leaves

Opening and closing of stomata

EXERCISE 15: Angiosperm Flower

and Seed

Dr. L Humphrieslhumphries@elcamino.edu

Spring 2005: Fundamentals of BiologySection 1107 Biology 10 4-Units

Sexual Reproduction in Flowering Plants

• Sexual reproduction requires gametes, often as egg and sperm.

• In flowering plants, the structures that produce the egg and sperm are located within the flower.

• Flowers have special structures to enable fertilization of egg by sperm.

Structure of Flowers

• The reproductive portions of a flower are the stamen, consisting of a stalk-like filament bearing an anther, and the pistil, made up of stigma, style, and ovary.

• The ovary contains one or more ovules.

• Sepals enclose a whorl of petals that are usually colored to attract pollinators.

Flower structure

Development of Seeds and Fruits

• In flowering plants, seeds are enclosed within a fruit that usually develops from the ovary.

• The ovary wall becomes the pericarp. • Fleshy fruits have a fleshy pericarp; dry

fruits have a dry pericarp. • An aggregate fruit such as blackberry is

derived from many ovaries on the flower.

• The ovule wall hardens and becomes the seed coat.

• The seed consists of the sporophyte embryo, stored food, and a seed coat.

• The ovary may develop into a fruit.

Fruit diversity

Common garden bean, a dicot

Corn, a monocot

The Petri Dish: GMO

Dr. L Humphrieslhumphries@elcamino.edu Spring 2005: Fundamentals of Biology

Section 1107 Biology 10 4-Units

Write a one page paper on GMO’s (genetically modified organism) using the following format. Be sure to include YOUR opinion

Please use the following format:1st Paragraph = Intro: What is a GMO, how are they made, and who makes them?

2nd Paragraph = Name a specific type of GMO that is either currently produced or is being researched and/or tested. (tomatoes, soybeans)

3rd Paragraph = Write AT LEAST a 5 sentence closing paragraph discussing how YOU feel about GMOs. Would you eat them? Do you eat them? Do you think they are safe or unsafe? If you could make one, what would it be? Etc…….

Genetic Engineering of Plants

• Various techniques introduce foreign DNA into protoplasts that are propagated in tissue culture.

• Adult plants are generated from these cells and could produce insecticide-resistant plants or plants that can grow in nutrient-limited soil.

• Plants can also be engineered to treat human diseases.

• Evolution encompasses common descent and adaptation to the environment.

• Due to common descent, all living things share common characteristics: they are made of cells, take chemicals and energy from the environment, respond to external stimuli, reproduce, and evolve.

• Many fields of biology give evidence that evolution has occurred.

Fossil Evidence• Fossils are the remains of past life, usually

consisting of hard parts, such as shells, bones, or teeth.

• Most fossils are found embedded in sedimentary rock.

• Sedimentation causes rock formation as particles accumulate in layers; any given stratum (layer) is older than the one above it, and younger than those below.

• Paleontologists are biologists who study fossils.

• Certain fossils serve as transitional links between groups.

• Such fossils allow paleontologists to deduce the sequence in which certain groups evolved (i.e., fishes evolved before amphibians, which came before reptiles, which evolved before both birds and mammals).

Transitional fossils

• Geological Time Scale• As a result of studying strata across the

earth, scientists have divided earth’s history into eras, periods, and epochs.

• There are two ways to date fossils:• Relative dating provides an approximate

age based on position of the fossil within rock strata.

• Absolute dating uses radioactive isotopes to measure the amount of radiation left in a fossil, yielding an actual age.

• Carbon 14 (14C) is the only radioactive isotope in organic matter.

• The amount of radioactivity remaining in a fossil can be compared with that of a modern sample to determine the age of a fossil.

• Radioactive isotopes decay at a known rate; the half-life of a radioactive isotope is the length of time it takes for half of the radioactive isotope to change into another stable element.

• Mass Extinctions• Extinction refers to the death of every

member of a species.• During a mass extinction, a large

percentage of species become extinct within a relatively short period of time.

• Mass extinctions occurred at the ends of the Ordovician, Devonian, Permean, Triassic, and Cretaceous periods.

• The Cretaceous mass extinction that led to the demise of dinosaurs was likely caused by an meteorite hitting the earth.

Dinosaurs

Biogeographical Evidence

• Biogeography is the study of the distribution of plants and animals throughout the world.

• The world’s six biogeographical regions have their own distinct mix of living things.

• Continental drift refers to the changing positions of the continents over time.

• Two hundred twenty-five million years ago, all the present land masses belonged to one continent (Pangaea).

• The distribution of plants and animals is consistent with continental drift.

• Organisms, such as certain seed plant groups or reptiles, are widely distributed throughout the world.

• Other groups, such as mammals that arose after the continents broke up, have great differences in species on different continents.

Continental drift

Anatomical Evidence• Despite dissimilar functions, all vertebrate

forelimbs contain the same sets of bones – this strongly suggests common descent.

• Structures that are similar because they are inherited from a common ancestor are homologous structures.

• Analogous structures are used for the same purpose but are not due to a common ancestor.

Bones of vertebrate forelimbs

• Vestigial structures are anatomical features that are fully developed in one group but reduced or nonfunctional in other, similar groups.

• Vestigial structures can be explained by common descent.

• The homology shared by vertebrates extends to their embryological development; all vertebrates have a dorsal notochord and paired pharyngeal pouches at some point.

• Evolution modifies existing structures.

Significance of developmental similarities

Biochemical Evidence

• All organisms have certain biochemicals in common.

• All use DNA, ATP, and many identical or nearly identical enzymes.

• Organisms use the same triplet code and the same 20 amino acids in proteins.

• This similarity is not necessary, but can be explained by common descent.

Significance of biochemical differences

• Once a plasma membrane formed, a protocell could have come into existence.

• Energy for the chemical reactions could have come from ultraviolet radiation, volcanoes, bombardment by comets, or from oceanic hydrothermal vents.

• The early atmosphere lacked oxygen and also a shield of ozone; it was not until photosynthesis evolved that oxygen was present in earth’s atmosphere.

Origin of the first cell(s)

Evolution of Small Organic Molecules

• Experiments by Stanley Miller in 1953 tested the hypothesis that small organic molecules were formed at the ocean’s surface.

• The first atmospheric gases (methane, ammonia, and hydrogen) were placed into a closed system, heated, and circulated past an electric spark to simulate lightning.

• A variety of amino acids and organic acids formed.

Miller’s experiment

Chemical evolution at hydrothermal vents

Macromolecules• There are three hypotheses concerning

how small organic molecules could give rise to macromolecules:

• The RNA-first hypothesis suggests that only the macromolecule RNA was needed to progress toward the first cell.

• RNA molecules (as ribozymes) can sometimes be both substrates and enzymes.

• The protein-first hypothesis, by Sidney Fox, suggested that amino acids collected in small puddles, and heat from the sun caused them to form proteinoids; when proteinoids were returned to water, they formed microspheres and had many properties of cells.

• This hypothesis assumes that DNA came after proteins.

• The third hypothesis, by Graham Cairns-Smith, suggests that clay was helpful in causing polymerization of both proteins and nucleic acids at the same time.

• Clay attracts small organic molecules and contains iron and zinc, which may have served as inorganic catalysts for polypeptide formation.

• This hypothesis suggests that RNA and polypeptides arose at the same time.

The Protocell• Before the first true cell, there would have

been a protocell that had a lipid-protein membrane and used energy metabolism.

• Fox has shown that if lipids are available to microspheres, the two form a lipid-protein membrane.

• Other work by Alexandr Oparin has shown that concentrated mixtures of macromolecules form coacervate droplets that a semipermeable boundary may form around.

Protocell anatomy

The Heterotroph Hypothesis• The protocell was likely a heterotroph,

absorbing small organic molecules from its environment.

• Natural selection would favor cells able to extract energy from carbohydrates to transform ADP to ATP.

• Fox has shown that microspheres have some catalytic ability, and Oparin found coacervates incorporate available enzymes.

The True Cell• A true cell is a membrane-bounded

structure that can carry on protein synthesis to produce the enzymes that allow DNA to replicate.

• It is possible that the sequence of DNA to RNA to protein developed in stages.

• Once the protocells acquired genes that could replicate, they became cells capable of reproducing, and evolution began.

Population Genetics

• A population is all the members of a species occupying a particular area at the same time; members of a population reproduce with each other to produce the next generation.

• The various alleles of all the gene loci in all the members make up the gene pool for the population.

• Hardy and Weinberg used a binomial expression to calculate the genotypic and phenotypic frequencies of a population:

• p2 + 2pq + q2 = 1• This expression is used to determine gene

frequencies at a given time and to predict gene frequencies in the future.

• If reproduction is completely random, the Hardy-Weinberg equation predicts the same gene pool frequencies generation after generation.

Using the Hardy-Weinberg equation

• The Hardy-Weinberg Law• The Hardy-Weinberg law states that

gene frequencies will stay the same in a large population over time provided:

1) There are no mutations or mutations are balanced.

2) There is no genetic drift; changes in allele frequencies due to chance alone are insignificant.

3) There is no gene flow – no migration of individuals in or out of the population.

4) Mating is random – individuals pair by chance and not by choice.

5) There is no selection – no selective force favors one genotype over another.

6) In real life, these conditions are rarely met, and microevolution, as seen by changing gene frequencies in Hardy-Weinberg equilibrium, occurs.

Microevolution

Five Agents of Evolutionary Change

• Mutations• Mutations provide new alleles and

therefore underlie all other mechanisms that produce variation.

• Mutations alone are unlikely to cause evolution; selective agents acting on heritable variation cause evolution.

• The adaptive value of a mutation depends on the environmental conditions.

• Genetic Drift• Genetic drift refers to changes in allele

frequencies of a gene pool due to chance; genetic drift has a much larger effect in a small population.

• The founder effect occurs when a few individuals leave the original population and begin a new population.

• A bottleneck effect is seen when much of a population is killed due to a natural disaster, and only a few remaining individuals are left to begin a new population.

Genetic drift

Founder effect

• Gene Flow• Gene flow is the movement of alleles

between populations, such as when individuals migrate from one population to another.

• Gene flow between two populations keeps their gene pools similar and prevents close adaptation to a local environment.

• Nonrandom Mating• Nonrandom mating occurs when

individuals pair up, not by chance, but according to genotypes and phenotypes.

• Inbreeding is an example of nonrandom mating.

• In a human population, inbreeding increases the frequency of recessive abnormalities.

• Natural Selection• Natural selection is the process by which

populations become adapted to their environment.

• Evolution by natural selection requires:

• Variation

• Inheritance of the genetic difference

• Differential adaptedness

• Differential reproduction.

• Three types of natural selection are known:

• Stabilizing selection – an intermediate phenotype is favored.

• Directional selection – one extreme phenotype is favored.

• Disruptive selection – both extreme phenotypes are favored over an intermediate phenotype.

Five-Kingdom System

• The five-kingdom system of classification is based on structural differences and also on modes of nutrition among the eukaryotes.

• The five kingdoms include:

• Monera (prokaryotes)

• Eukaryotic kingdoms of Protista, Fungi, Plantae, and Animalia.

Five-kingdom system of classification

Three-Domain System

• The three-domain system recognizes three domains: Bacteria, Archaea, and Eukarya.

• This system of classification is based on biochemical differences that show there are three vastly different groups of organisms.

Three-domain system of classification

The three domains of life

• Chemical evolution likely resulted in the first cells.

• Inorganic chemicals derived from the primitive atmosphere reacted to form simple organic molecules.

• The RNA-first and protein-first hypotheses seek to explain how the first protocell arose.

• Eventually, the DNA → RNA → protein self-replicating system evolved, as did the first true cell.

• Evolution is a process that involves changes in gene frequencies in a population according to Hardy-Weinberg equilibrium.

• Equilibrium is maintained unless disrupted by mutations, genetic drift, gene flow, nonrandom mating, or natural selection.

• Speciation requires geographic isolation followed by reproductive isolation.

• There are two hypotheses regarding the pace of evolution – phyletic gradualism and punctuated equilibrium.

• Classification involves the assignment of species to a hierarchy of categories: species, genus, family, order, class, phylum, kingdom, and domain.

• The three-domain system recognizes three domains: Bacteria, Archaea, and Eukarya.