plant biology Flashcards

Question

Examine and learn the anatomy of a root. Know the function of and be able to identify the root cap, zone of cell division, xylem, phloem, endodermis, and root hairs.

Answer 1

Root Anatomy and Functions Root Cap • A tough, protective covering at the tip of the root. • Protects the delicate growing cells as the root pushes through the soil. Zone of Cell Division • Located just behind the root cap. • New cells are made here by mitosis in the apical meristem (growth tissue). Xylem • Found in the center of the root. • Transports water and minerals up from the roots to the rest of the plant. Phloem • Located around or near the xylem. • Transports sugars and nutrients from the leaves down to the roots and other parts. Endodermis • A single layer of tightly packed cells that forms a boundary around the vascular tissue. • Regulates what enters the xylem (like a filter). Root Hairs • Tiny extensions of root cells near the tip of the root. • Increase surface area to absorb more water and nutrients from the soil. ⸻ Quick Summary • Root cap = protects. • Zone of cell division = makes new cells. • Xylem = moves water up. • Phloem = moves food down. • Endodermis = controls entry to xylem. • Root hairs = absorb water and nutrients.

Answer 2

Root Hairs and Their Significance • Root hairs are tiny extensions of root epidermal cells. • They are very thin and long, which gives them a huge surface area. • They increase water and mineral absorption because they reach into the tiny spaces between soil particles. • More surface area means the plant can absorb much more water and nutrients than it could with just the main root alone. ⸻ Quick Summary • Root hairs = tiny structures that grab water and minerals from the soil. • They are essential for keeping the plant hydrated and fed.

Answer 3

Route of Water Movement from Soil to Leaves 1. Soil to Root Hairs • Water enters root hairs by osmosis (water moves from high concentration in the soil to lower concentration inside the root). 2. Root Hairs to Cortex • Water travels through the cortex (the ground tissue of the root) by moving cell to cell or around cells. 3. Through the Endodermis • Water must pass through the endodermis (which controls what gets into the plant’s vascular system). • It passes through the Casparian strip, a waterproof barrier forcing water into cells (not just between them). 4. Into the Xylem • After the endodermis, water enters the xylem vessels — the tubes that carry water upward. 5. Up the Stem and Into the Leaves • Water is pulled upward by transpiration (evaporation of water from leaf stomata). • Cohesion (water sticking to water) and adhesion (water sticking to xylem walls) help move the water up. 6. Evaporation at the Leaves • Water finally exits through stomata on the leaves into the air. ⸻ Quick Summary • Soil → Root hairs → Cortex → Endodermis → Xylem → Leaves → Air

Answer 4

Leaf Anatomy and Functions • Upper Epidermis • Outer protective layer on the top of the leaf. • Covered by a waxy cuticle to prevent water loss. • Leaf Vein (Vascular Bundle) • Contains xylem (moves water to the leaf) and phloem (moves sugars away from the leaf). • Provides support and transport. • Stomata (singular = stoma) • Tiny pores mostly on the underside of the leaf. • Allow gas exchange: CO₂ in, O₂ and water vapor out. • Open and close with guard cells. • Palisade Mesophyll • Layer of tightly packed cells right under the upper epidermis. • Main site of photosynthesis — lots of chloroplasts to capture sunlight. • Spongy Mesophyll • Loosely packed cells with air spaces between them. • Helps with gas movement (CO₂ and O₂) inside the leaf. ⸻ Quick Summary • Upper epidermis = protection. • Vein = transport water and sugars. • Stomata = gas exchange. • Palisade mesophyll = photosynthesis. • Spongy mesophyll = gas circulation.

Answer 5

Stomata and Their Role • Stomata are tiny openings mainly on the underside of leaves. • Each stoma is surrounded by two guard cells that open and close the pore. ⸻ Role in Water Movement • When stomata are open, water vapor escapes from inside the leaf into the air. • This process is called transpiration. • Transpiration creates a pull that draws water upward from the roots through the xylem. ⸻ Role in Gas Exchange • When stomata are open, they allow carbon dioxide (CO₂) to enter for photosynthesis. • They also let oxygen (O₂) (waste from photosynthesis) exit into the air. ⸻ Quick Summary • Water movement: Stomata let water evaporate (pulls water up). • Gas exchange: Stomata let CO₂ in and O₂ out.

Answer 6

Plant Adaptations Based on Water Availability 1. Xerophytes (plants in dry environments like deserts) • Thick cuticle: Reduces water loss. • Small or no leaves: Lowers evaporation (some have spines instead, like cacti). • Deep or wide-spreading roots: Reach deep or far for water. • Stomata open at night (CAM photosynthesis) to save water. 2. Mesophytes (plants in moderate environments) • Normal-sized leaves: Good for regular sunlight and rainfall. • Regular stomata activity: Open during the day for gas exchange. • Balanced root systems: Not extremely deep or shallow. 3. Hydrophytes (plants in water or wet environments) • Thin or no cuticle: No need to prevent water loss. • Large air spaces in tissues: Help float and move oxygen to underwater parts. • Stomata on upper leaf surface: Since the bottom is in water, they open on top. ⸻ Quick Summary • Xerophytes: Save water. • Mesophytes: Balanced for moderate conditions. • Hydrophytes: Handle lots of water easily.

Answer 7

Mineral Transport in Plants • Minerals from the soil enter root hairs mainly by active transport. (Because minerals are often more concentrated inside the plant than in the soil, they need energy to move in.) • After entering root hairs, minerals move cell-to-cell through the cortex toward the xylem. • At the endodermis, minerals are filtered — the plant controls which minerals are allowed into the xylem. • Once inside the xylem, minerals travel upward with water by the transpiration pull (cohesion-tension model). ⸻ Quick Summary • Active transport moves minerals into the root. • Xylem carries minerals up with the water flow.

Answer 8

Functions of Key Mineral Nutrients in Plants • Nitrogen (N) • Needed for making proteins and chlorophyll (important for growth and green leaves). • Phosphorus (P) • Important for energy transfer (ATP) and root development. • Potassium (K) • Helps regulate water balance and opening and closing of stomata. • Calcium (Ca) • Builds cell walls and helps with cell division. • Magnesium (Mg) • Central atom in chlorophyll, needed for photosynthesis. • Iron (Fe) • Needed to make chlorophyll and for enzyme functions. ⸻ Symptoms of Mineral Deficiencies • Nitrogen deficiency: • Yellowing leaves (especially older leaves first). • Phosphorus deficiency: • Purple or dark green leaves, stunted growth. • Potassium deficiency: • Brown edges on leaves, weak stems. • Calcium deficiency: • Deformed or crumbling new leaves. • Magnesium deficiency: • Yellowing between veins of older leaves (leaves look striped). • Iron deficiency: • Yellowing between veins of young leaves (new leaves look pale). ⸻ Quick Summary • Different minerals have different jobs. • Deficiencies show as color changes, poor growth, or leaf damage.

Answer 9

Symbiotic Relationship of Plants and Bacteria • Certain plants (mostly legumes, like peas and beans) form a mutualistic relationship with nitrogen-fixing bacteria (like Rhizobium). • The bacteria live inside root nodules (small bumps on the plant roots). ⸻ Role of Symbiotic Nitrogen Fixation • Bacteria take nitrogen gas (N₂) from the air (which plants can’t use) and convert it into ammonia (NH₃), a form plants can absorb and use to make proteins. • In return, the plant gives the bacteria sugars and a safe home in the root nodules. ⸻ Quick Summary • Bacteria fix nitrogen → Plants get usable nitrogen → Bacteria get food and shelter.

Answer 10

Symbiotic Relationship of Plants and Fungi • Most plants form a mutualistic relationship with fungi called mycorrhizae. • The fungi grow around or inside the plant’s roots. ⸻ Role of Mycorrhizae • Fungi help the plant absorb more water and minerals (especially phosphorus) from the soil. • Plants provide the fungi with sugars made during photosynthesis. • This partnership makes plants healthier, stronger, and more drought-resistant. ⸻ Quick Summary • Fungi boost water and nutrient uptake. • Plants feed fungi with sugars.

Answer 11

Transport of Organic Nutrients in Plants • Organic nutrients (mainly sugars made during photosynthesis) are transported through the phloem. • This movement is called translocation. ⸻ How It Works (Pressure-Flow Model) 1. Sugars are made in source tissues (like leaves). 2. Sugars are actively loaded into phloem sieve tubes. 3. Water from nearby xylem moves into the phloem by osmosis, creating high pressure. 4. The pressure pushes the sugary fluid through the phloem toward sink tissues (like roots, fruits, or growing shoots) that need or store the sugars. 5. Sugars are unloaded at the sink, and water returns to the xylem. ⸻ Quick Summary • Phloem moves sugars from source (leaf) to sink (root, fruit, etc.) using pressure differences.

Answer 12

What is the Greenhouse Effect? • The greenhouse effect is when certain gases trap heat in Earth’s atmosphere, keeping the planet warm enough to support life. ⸻ Causes of the Greenhouse Effect • Sunlight reaches Earth; some of it is reflected back into space. • Some of it is absorbed by Earth’s surface and then re-radiated as heat (infrared radiation). • Greenhouse gases like carbon dioxide (CO₂), methane (CH₄), and water vapor trap some of that heat instead of letting it escape into space. Major greenhouse gases include: • Carbon dioxide (CO₂) • Methane (CH₄) • Nitrous oxide (N₂O) • Water vapor (H₂O) ⸻ Consequences of the Greenhouse Effect • Natural greenhouse effect: • Good — keeps Earth at a livable temperature. • Enhanced (human-caused) greenhouse effect: • Too much heat trapped → global warming. • Rising sea levels from melting ice. • More extreme weather (floods, droughts, hurricanes). • Changes in ecosystems and plant/animal life. ⸻ Quick Summary • Normal greenhouse effect = good (life possible). • Too much greenhouse effect = bad (climate problems).

Answer 13

Changes in Atmospheric CO₂ Through Geologic Time • Over millions of years, CO₂ levels have risen and fallen naturally. • Very high CO₂ during times like the age of dinosaurs (hotter Earth). • Lower CO₂ during ice ages (colder Earth). • Natural changes were caused by volcanoes, weathering of rocks, ocean absorption, and plant life. ⸻ Changes in CO₂ Over the Past 200 Years • Since the Industrial Revolution (~1800s), CO₂ levels have rapidly increased. • Main cause: Burning fossil fuels (coal, oil, natural gas) and deforestation (cutting down forests). • CO₂ levels have risen from about 280 parts per million (ppm) (pre-1800s) to over 420 ppm today — the highest in hundreds of thousands of years. ⸻ How CO₂ Levels Are Related to Climate • More CO₂ = more heat trapped = warmer global temperatures. • As CO₂ rises, Earth’s average temperature increases (global warming). • Past high CO₂ periods matched with hotter climates; low CO₂ periods matched with ice ages. ⸻ Quick Summary • Long-term: CO₂ levels changed naturally with Earth’s cycles. • Past 200 years: Human activities caused a sharp CO₂ rise. • More CO₂ = Warmer Earth.

Answer 14

Major Causes of Recent Increases in Atmospheric CO₂ (Last 200 Years) 1. Burning Fossil Fuels • Coal, oil, and natural gas are burned for energy, releasing carbon dioxide. • Major sources: power plants, cars, planes, and factories. 2. Deforestation • Cutting down forests reduces the number of trees that absorb CO₂. • Trees store carbon, so when they are burned or decay, they release CO₂. 3. Industrial Processes • Making cement, steel, and other materials releases CO₂ during production. 4. Agriculture • Some farming activities (like soil plowing and fertilizer use) increase CO₂ and other greenhouse gases. ⸻ Quick Summary • Burning fuels, cutting forests, industrial production, and farming have all pushed CO₂ levels up.

Answer 15

Consequences of Higher CO₂ Levels on Plant Growth 1. Faster Growth (sometimes) • Higher CO₂ can make some plants grow faster, because CO₂ is needed for photosynthesis. 2. Bigger Leaves but Weaker Tissues • Plants may have larger leaves but thinner, weaker tissues, making them more vulnerable to pests or drought. 3. Lower Nutritional Value • Crops grown in high CO₂ often have less protein, iron, and zinc, reducing their nutritional quality. 4. Different Species Responses • Some plants (like weeds) benefit more from high CO₂ than crops, possibly leading to more weed problems. 5. Water Use Efficiency Improves • Plants may lose less water because they can keep stomata more closed, helping them survive dry conditions. ⸻ Quick Summary • More CO₂ = faster growth, but weaker plants, poorer nutrition, and more weeds.

Answer 16

Biological Factors That Limit Solar Energy Conversion into Food 1. Light Absorption • Plants don’t absorb all wavelengths of sunlight — mostly only red and blue light, so some energy is lost. 2. Photosynthetic Efficiency • Even under perfect conditions, plants only convert about 1–2% of sunlight into chemical energy (sugars). 3. Respiration • Plants use some of their own energy for growth and maintenance, not just storing it as food. 4. Water and Nutrient Availability • Without enough water or minerals, plants can’t photosynthesize at full speed. 5. Temperature Extremes • If it’s too hot or too cold, photosynthesis slows down or stops. 6. Damage from Herbivores or Disease • Insects, animals, or fungal infections can reduce leaf area or damage plants, limiting energy capture. ⸻ Quick Summary • Not all light used, low efficiency, energy used for living, and environmental limits all reduce food production.

Answer 17

2nd Law of Thermodynamics and Food Production • The 2nd Law of Thermodynamics says that energy is always lost as heat when it changes form. • In food production, energy from the Sun is captured by plants, but most of it is lost at each step: • Plants only store a small part of the sunlight they receive. • When animals eat plants, they lose even more energy as heat through movement, digestion, and metabolism. • Only a tiny fraction of the original solar energy becomes usable food energy for humans. ⸻ Why It Matters for Feeding a Growing Population • Producing plant-based foods is more energy-efficient because it loses fewer steps. • Raising animals (meat production) is less efficient because it loses more energy between the plants and the final food. • To feed more people, efficient use of energy (like eating more plants and improving farming) is important. ⸻ Quick Summary • Energy is lost at every step. • More plant-based food = more efficient use of solar energy.

Answer 18

Implications of the 2nd Law of Thermodynamics: Meat vs. Grain • The 2nd Law says that energy is always lost (mostly as heat) when it changes from one form to another. • When humans eat grains (plants), they get energy directly from the Sun’s stored energy (only one major step). • When humans eat meat, the energy had to first pass through animals (plants → animals → humans), meaning even more energy is lost at each step. ⸻ Why It Matters • Producing meat uses more energy, land, and water because animals must be fed lots of plants to grow. • Producing grains is more efficient — more people can be fed with the same amount of land and energy. ⸻ Quick Summary • Grain = direct, efficient energy use. • Meat = indirect, wasteful energy use. • Feeding more people is easier with plant-based foods.

Answer 19

How Population Growth Affects Food Needs • As the human population increases, the total amount of food needed also increases. • More people means we need more crops, more animals, and more water, land, and energy to produce food. ⸻ Challenges to Providing Enough Food • Limited resources: • Good farmland, fresh water, and fertilizer are limited. • Land use pressure: • Expanding farms often leads to deforestation and loss of natural ecosystems. • Environmental impact: • More farming can cause pollution, soil erosion, and climate change, making farming harder over time. • Inefficiency: • Producing meat uses much more land and energy than producing grains or vegetables. • Food distribution: • Even if enough food is produced, unequal distribution can leave some areas hungry while others have surpluses. ⸻ Quick Summary • More people = more food needed. • Strains on land, water, and environment make feeding everyone harder unless farming becomes more efficient and sustainable.

Answer 20

Factors That Limit Food Production 1. Limited Farmland • There’s only so much good land for farming; cities and deserts can’t easily grow food. 2. Water Shortages • Crops need a lot of water, and freshwater supplies are already overused in many places. 3. Soil Degradation • Overfarming, erosion, and pollution can damage soil, making it less productive. 4. Climate Change • Extreme weather (droughts, floods, heatwaves) harms crops and reduces yields. 5. Pests and Diseases • Insects, fungi, and plant diseases can destroy crops faster than farmers can grow them. 6. Energy Costs • Farming depends on energy (for machines, fertilizers, irrigation), and high costs can limit food production. 7. Loss of Biodiversity • Growing only a few types of crops (monoculture) can make farms more vulnerable to pests and disease. 8. Political and Economic Issues • Wars, trade restrictions, and poverty can block food production or food distribution even if enough is grown. ⸻ Quick Summary • Natural limits, environmental damage, and human problems all make it harder to produce enough food.

Answer 21

Inverse Relationship Between Plant Water Conservation and Photosynthesis • Plants need to open their stomata to let in carbon dioxide (CO₂) for photosynthesis. • But when stomata are open, water vapor escapes — leading to water loss (transpiration). So: • If plants keep stomata open → more photosynthesis, but more water loss. • If plants close stomata to save water → less photosynthesis, so less food energy produced. ⸻ Ecological Consequences 1. Slower Plant Growth • In dry environments, plants grow slower because they must keep stomata closed more often. 2. Lower Crop Yields • Less photosynthesis means smaller harvests, especially during droughts. 3. Changes in Ecosystems • Drought-tolerant plants (like cacti) may outcompete less water-efficient plants, changing the types of plants and animals in an area. 4. Less Carbon Capture • If plants photosynthesize less, they absorb less CO₂, making it harder to slow climate change. ⸻ Quick Summary • Saving water = less photosynthesis = slower growth, smaller harvests, and ecosystem changes.

Answer 22

Three Metabolic Pathways Plants Use to Fix CO₂ 1. C₃ Pathway (C₃ Photosynthesis) • Most common (used by most plants like wheat, rice, and trees). • CO₂ is directly fixed into a 3-carbon compound called 3-PGA. • Works best in cool, wet environments. • Problem: Loses efficiency in hot, dry conditions because of photorespiration (wasting energy when stomata close). 2. C₄ Pathway (C₄ Photosynthesis) • Used by plants like corn and sugarcane. • CO₂ is first fixed into a 4-carbon compound (oxaloacetate). • Special leaf structure (bundle sheath cells) separates carbon fixation from photosynthesis, reducing photorespiration. • Works well in hot, sunny environments. 3. CAM Pathway (Crassulacean Acid Metabolism) • Used by desert plants like cacti and pineapples. • Stomata open at night (to take in CO₂ and store it) and close during the day (to save water). • Photosynthesis happens during the day using stored CO₂. • Best for very dry conditions. ⸻ Quick Summary • C₃: Most plants, good in cool/wet, bad in hot/dry. • C₄: Hot, sunny areas; very efficient. • CAM: Dry deserts; saves water by opening stomata at night.

Answer 23

C₃ Pathway Benefits: • Simple and energy-efficient under cool, moist conditions. • Works well when water is available and temperatures are moderate. Costs: • Photorespiration (wasting energy and carbon) happens when it’s hot and dry because stomata close to save water. • Less efficient in warm climates. ⸻ C₄ Pathway Benefits: • Minimizes photorespiration even in hot, sunny environments. • Very efficient at capturing CO₂ and producing energy in high light and heat. Costs: • Requires extra energy (ATP) to fix CO₂ into a 4-carbon molecule. • More complex leaf structure needed (bundle sheath cells). ⸻ CAM Pathway Benefits: • Excellent water conservation — stomata open only at night, reducing water loss. • Ideal for extremely dry, desert environments. Costs: • Slower growth because CO₂ is collected at night and stored, limiting how much can be processed during the day. • Energy costly to store and later use CO₂. ⸻ Quick Summary • C₃: Low energy use, but bad in heat. • C₄: Good in heat, but costs more energy. • CAM: Great water saver, but slow growth.

Answer 24

Effects of Climate Change on Ecosystem Productivity • Increased temperatures, droughts, and changing rainfall patterns can reduce plant growth (lower primary productivity). • Faster CO₂ rise can sometimes speed up plant growth, but if water, nutrients, or temperatures are bad, growth still declines. • Extreme events (like wildfires, storms, and heatwaves) can damage plants and lower ecosystem productivity even more. ⸻ How This Affects Heterotrophic Organisms (Animals, Fungi, etc.) • Heterotrophs (organisms that eat plants or other animals) depend on plants for food energy. • If plants grow less → less food is available for herbivores (plant-eaters). • If herbivores decline, carnivores (meat-eaters) will also decline because their food sources shrink. • Whole food webs become weaker or collapse if plant productivity drops too much. ⸻ Quick Summary • Less plant growth = less food = decline of animals across the food chain.

Answer 25

Implications of Limits on Agricultural Production 1. Food Shortages • If crop yields cannot keep up with population growth, some areas will face hunger and malnutrition. 2. Higher Food Prices • Scarcity of food leads to higher prices, making it harder for poor populations to afford enough to eat. 3. Greater Pressure on Land and Water • Farmers may clear more forests and overuse water to grow more food, causing environmental damage. 4. Increased Dependence on Technology • Need for genetically modified crops, better irrigation, and efficient fertilizers will grow — but not every region can access or afford them. 5. Global Inequality • Wealthier countries will likely be able to adapt better, while poorer countries may suffer more food insecurity. 6. Potential for Conflict • Competition over land, water, and food could lead to political tension, migration, or even conflicts. ⸻ Quick Summary • Limits on farming = less food, higher prices, more inequality, and more environmental strain.

plant biology Flashcards

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