Plants Flashcards
1
Q
Characteristics of the origins of the Earth
A
- Earth is about 4.6 billion years old
- Earth sustained a meteoroid bombardment that ended about 3.8 billion years ago
- Vast chunks of rubble may have slammed into the planet keeping it hot.
- As earth began to cool: – violent storms, lightening, widespread volcanism and boiling water
2
Q
Stromatolites
def
A
- fossilized microbial mats consisting of layers of filamentous microbes
- about 3.5 billion years old
- present day: found in shallow, warm oceans (Australia and Bahamas) and formed by cyanobacteria.
3
Q
Origin of organic molecules
A
- Organic molecules formed by the action of lightning, rain and solar energy on gases in the environment may have accumulated in the oceans.
- Some organic molecules have a tendency to aggregate in groups (Form of droplets similar to oil in water)
- Such assemblages of organic molecules appear to have been the forerunners of primitive cells, the first forms of life.
- As they evolved, they became more complex.
- With increasing complexity, they may have acquired the ability to grow, reproduce, and to pass on their characteristics to subsequent generations
- These three properties and cellular organization characterize all living things on earth
4
Q
Heterotrophs
def
A
- depend on outside source of organic molecules as their energy source.
- As primitive heterotrophs increased in number, they may have begun to use up the complex molecules.
- As a result, these organic molecules may have become less abundant.
5
Q
What caused autotrophs to appear?
A
- Competition for resources began with primitive heterotrophs that were increasing in numbers.
- Cells that could make efficient use of limited energy sources were more likely to survive than others
- Autotrophs evolved: Cells may have evolved to make their own energy rich molecules.
6
Q
What makes an autotroph successful?
A
- The most successful autotrophs: – with a system for making direct use of sun’s energy: Photosynthesis – required complex pigment system to capture the light energy and a way to store energy in an organic molecule.
- Evidence for the activities of photosynthetic organisms has been found in 3.4 billion years old rocks (100 million years after the first fossil evidence)
- With the origin of autotrophs, the flow of energy in the biosphere came to assume its modern form. – radiant energy from the sun channelled through the photosynthetic autotrophs to all other forms of life.
7
Q
How did photosynthesis alter earth’s atmosphere, and influence the evolution of life?
A
- Photosynthesis involves splitting of water molecules and releasing O2
- Prior to 2.2 billion years ago, the oxygen released into the oceans and lakes reacted with dissolved iron and precipitated as iron oxides.
- From about 2.7-2.2 billion years ago, oxygen began to accumulate in the atmosphere.
- About 700 million years ago, atmospheric O2 levels increased markedly, and began to approach modern levels by 570-510 million years ago.
- The increase in O2 level had two important consequences: – Outer layer O2 converted to O3 and absorbed UV
- by about 450 million years ago, O3 protected organisms sufficiently to survive in the surface water: – Increase in free O2opened the way to a much more efficient utilization of energy rich organic molecules through aerobic respiration.
- Glucose -> Aerobic respiration -> 36 ATP Glucose -> Anaerobic respiration -> 2ATP
8
Q
Before and after Accumulation of O2 in the athmosphere
A
- Before accumulation of O2 in the atmosphere: – the only cells that existed were prokaryotic (Archea and bacteria). •Some of these are heterotrophic and some (cyanobacteria) are autotrophic.
- After accumulation of free O2 in the atmosphere: – appearance of Eukaryotic cells • cells with nuclear envelopes, complex chromosomes, organelles surrounded by membranes
9
Q
How did the seashore play a major role in the evolution of organisms?
A
- Early in evolution, the principal photosynthetic organisms were microscopic cells floating below the surface of the sunlit waters.
- Over time, they depleted the mineral resources of the open ocean
- Life began to develop more abundantly toward the shores. – the waters were rich in nitrates and minerals carried down from mountains by rivers and streams.
- The rocky coast presented a much more complicated environment
- Living organisms became increasingly complex in structure and more diversified.
- Organisms evolved into many cells that were linked together to form an integrated multicellular body.
- These primitive organisms represent the early stages of the evolution of plants, fungi and animals.
- On the turbulent shore, multi-cellular photosynthetic organisms were better able to maintain their position against the action of the waves and overcome challenges of the environment.
10
Q
Describe colonization of land by organisms
A
- Evolution of new forms of organisms with relatively strong cell walls for support, as well as specialized structures to anchor their bodies to the rocky surfaces.
- As their size increased, specialized food conducting tissues evolved to connect upper photosynthetic parts to lower non-photosynthetic structures. Colonization of the land was associated with the evolution of structures to obtain water and minimize water loss
- Requirements of photosynthetic organisms: – light, water, CO2, O2 for respiration, and few minerals. On land, water is the limiting factor - Roots anchor the plant in the ground and collect water. - stems provide support for the photosynthetic organs. - Continuous stream of water moves upward, and out through leaves.
11
Q
How do plants retain water?
A
- Epidermis is covered with waxy cuticle to retard water loss. Cuticle prevents gas exchange, therefore stomata evolved.
- In perenials, stem may be thickened and woody and covered with cork, which retards water loss.
- Xylem for water transport and Phloem for food transport
- Meristem for continuous growth – (Apical for primary, and lateral for secondary growth)
- Drought resistant spores for reproduction
- Complex, multicellular structures to protect reproductive cells from desiccation.
- In seed plants, embryo enclosed within a specialized covering (seed coat).
12
Q
What did land plants evolve from?
A
Green algae called charophytes are the closest relatives of land plants
13
Q
Why do we think land plants evolved from charophytes?
A
- Many characteristics of land plants also appear in a variety of algal clades
- However, land plants share four key traits with only charophytes
- Rings of cellulose-synthesizing complexes
- Peroxisome enzymes
- Structure of flagellated sperm
- Formation of a phragmoplast
- Comparisons of both nuclear and chloroplast genes point to charophytes as the closest living relatives of land plants
- Note that land plants are not descended from modern charophytes, but share a common ancestor with modern charophytes
14
Q
Adaptations Enabling the Move to Land
A
- In charophytes a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out
- Sporopollenin is also found in plant spore walls
- The movement onto land by charophyte ancestors provided unfiltered sun, more plentiful CO2, nutrient-rich soil, and few herbivores or pathogens
- Land presented challenges: a scarcity of water and lack of structural support
- The accumulation of traits that facilitated survival on land may have opened the way to its colonization by plants
- Systematists are currently debating the boundaries of the plant kingdom
- Some biologists think the plant kingdom should be expanded to include some or all green algae
- Until this debate is resolved, we define plants as embryophytes, plants with embryos
15
Q
Four key traits appear in nearly all land plants but are absent in the charophytes
A
- Alternation of generations and multicellular, dependent embryos
- Walled spores produced in sporangia
- Multicellular gametangia
- Apical meristems
