Resource Acquisition, Nutrition, and Transport in Vascular Plants

Xylem and Phloem: Plant Transport Systems

Plants use specialized tissues to transport water, minerals, and products of photosynthesis throughout their bodies.

• Xylem: Transports water and minerals from roots to shoots.

• Phloem: Transports sugars and other products of photosynthesis from sources (leaves or storage organs) to sinks (areas of need or storage). Transport can occur in both directions.

Example: Sucrose is actively transported in phloem cells via cotransport with H+ ions.

Trade-offs in Plant Morphology

Plants face trade-offs between maximizing photosynthesis and minimizing water loss.

• Shoot height vs. branching: Taller shoots may capture more light but have fewer branches.

• Leaf morphology & orientation: Leaves emerge in a spiral to minimize shading.

Membrane Transport in Plants

Plants use active transport and ion channels to move solutes across cell membranes.

• Active transport: Uses H+ ions and proton pumps to establish membrane potential. Requires energy and moves solutes against their concentration gradient.

• Cotransport: Sucrose is moved against its gradient with H+ moving down its electrochemical gradient.

• Ion channels: Allow selective passage of ions (e.g., K+ channels regulate stomata).

• Electric signals: Ion channels produce electric signals for plant integration, similar to animal nervous systems but much slower.

Water Movement: Osmosis and Water Potential

Water moves in plants via osmosis, driven by differences in water potential.

• Osmosis: Diffusion of water across a membrane.

• Water potential (Ψ): Predicts direction of water flow; moves from high to low potential.

• Solute potential (Ψs): More solutes decrease water potential.

• Pressure potential (Ψp): Physical pressure on a solution; positive in living cells due to turgor pressure.

Equation:

• Turgid: Water flows in; cell is stiff.

• Wilted/Plasmolysis: Water flows out; protoplast shrinks.

• Aquaporins: Proteins that facilitate water transport across membranes.

Bulk Flow

Bulk flow is the movement of liquids in response to a pressure gradient, independent of solute concentration.

• Occurs in xylem (tracheids & vessel elements) and phloem (sieve-tube elements).

• Bulk flow is faster than diffusion.

Essential Elements and Plant Nutrition

Plants require certain elements for growth, function, and reproduction.

• Macronutrients: Needed in large amounts (C, O, H, N, S, K, Ca, Mg).

• Micronutrients: Needed in small amounts (Cl, Fe, Mn, B, Zn, Cu, Ni, Mo; Na for CAM/C4 plants).

• Hydroponic culture: Used to identify essential elements.

• Fertilization: N-P-K ratio; can cause environmental issues via runoff.

• Organic fertilizer: Must be decomposed to inorganic nutrients for absorption.

Soil and Mineral Availability

Soil composition and pH affect mineral availability for plants.

• Humus: Organic matter from decomposition.

• Loams: Most fertile topsoil; mix of sand, silt, clay.

• Cation exchange: H+ displaces mineral cations from soil particles for absorption.

Mutualisms in Plant Nutrition

Plants form mutualistic relationships with fungi and bacteria to enhance nutrient acquisition.

• Rhizobacteria: Live in rhizosphere, promote plant growth.

• Endophytes: Live within plant tissues, provide benefits.

• Mycorrhizae: Fungal associations with roots; ectomycorrhizae (sheath over root), arbuscular (penetrate cortex).

Nitrogen Cycle and Fixation

Nitrogen is essential for plant growth and is made available through bacterial activity.

• Plants use nitrogen as NH4+ and NO3-.

• Ammonification: Decomposers convert organic N to NH4+.

• Nitrification: NH4+ → NO2- → NO3- by bacteria.

• Nitrogen fixation: Bacteria (e.g., Rhizobium) convert N2 to NH3.

Specialized Plant Adaptations

• Epiphytes: Grow on other plants, gather own nutrients.

• Parasitic plants: Absorb nutrients from host via haustoria.

• Carnivorous plants: Obtain nitrogen from insects.

Xylem Transport: Cohesion-Tension Hypothesis

Xylem sap is transported via transpiration, driven by water potential differences and cohesion of water molecules.

• Transpiration pulls water up through xylem.

• Cohesion (hydrogen bonds) maintains water column.

Reproduction and Domestication of Flowering Plants

Alternation of Generations in Angiosperms

Angiosperms alternate between diploid sporophyte and haploid gametophyte generations.

• Sporophyte: Diploid, produces haploid spores via meiosis.

• Gametophyte: Haploid, produces gametes via mitosis.

• Fertilization forms diploid zygote, which develops into new sporophyte.

Flower Structure and Function

Flowers are reproductive organs characterized by carpels, stamens, petals, and sepals.

• Carpels (pistils): Ovary, style, stigma; contain ovules.

• Stamens: Filament and anther; produce pollen.

• Petals: Attract pollinators.

• Sepals: Protect flower buds.

• Complete flowers: Have all four parts; incomplete lack one or more.

ABC Hypothesis of Flower Development

ABC genes control the identity of floral organs.

• A: Sepals & petals

• B: Petals & stamens

• C: Stamens & carpels

Female Gametophyte (Embryo Sac) Development

• Megasporocyte undergoes meiosis → four megaspores (one survives).

• Surviving megaspore divides mitotically → embryo sac with eight nuclei in seven cells.

• Synergids, antipodal cells, polar nuclei, and egg cell are present.

Male Gametophyte (Pollen Grain) Development

• Microsporocytes in anther undergo meiosis → microspores.

• Microspores undergo mitosis → pollen grain (generative cell and tube cell).

Pollination and Double Fertilization

• Pollen transferred from anther to stigma.

• Pollen tube delivers sperm to embryo sac.

• Double fertilization: One sperm fertilizes egg (zygote), other fuses with polar nuclei (endosperm).

Seed and Fruit Formation

• Ovule becomes seed; ovary becomes fruit.

• Seed contains embryo, stored food, protective coat.

• Fruit types: simple, aggregate, multiple, accessory.

Asexual and Sexual Reproduction in Plants

• Asexual: Fragmentation, apomixis.

• Sexual: Generates variation; beneficial in variable environments.

• Selfing prevention: Dioecious plants, self-incompatibility.

Genetic Modification and Domestication

• Transgenic plants: Engineered to express genes from other species.

• Benefits: Increased crop yield, reduced hunger.

• Drawbacks: Potential health risks, environmental concerns.

Plant Responses to Internal and External Signals

Cell Signaling in Plants

Plants respond to stimuli via reception, transduction, and response.

• Reception: Detect stimuli (touch, light, chemicals).

• Transduction: Relay and amplify signal.

• Response: Change in growth or development.

Plant Hormones and Their Functions

Photomorphogenesis and Photoreceptors

• Photomorphogenesis: Light triggers plant growth and development.

• Etiolation: Growth in darkness; de-etiolation occurs upon exposure to light.

• Photoreceptors: Blue-light (phototropism, stomatal opening), phytochromes (seed germination, shade avoidance).

Circadian Rhythms and Photoperiodism

• Circadian rhythms: 24-hour cycles independent of environment.

• Photoperiodism: Response to day/night length; affects flowering.

• Short-day, long-day, and day-neutral plants.

Mechanical and Environmental Responses

• Thigmomorphogenesis: Changes in form due to mechanical perturbation.

• Thigmotropism: Directional growth in response to touch.

• Heat-shock proteins: Protect proteins during high heat.

• Antifreeze proteins: Prevent ice formation in cold.

Plant Defenses Against Herbivory

• Physical (spines, thorns), chemical (toxins), and behavioral (recruit predators) defenses.

The Internal Environment of Animals: Organization and Regulation

Animal Anatomy and Physiology

Animals are composed of four main tissue types, each with specialized functions.

• Epithelial: Covers body surfaces, lines organs.

• Connective: Supports and binds tissues; includes blood, adipose, fascia.

• Muscle: Skeletal (voluntary), cardiac (heart), smooth (involuntary).

• Nervous: Neurons and glial cells; processes and transmits information.

Regulation and Homeostasis

• Stimulus: Triggers change in activity.

• Response: Change in activity due to stimulus.

• Homeostasis: Maintenance of internal balance.

• Requires sensor, control center, and effector.

Endocrine and Nervous Systems

• Endocrine: Hormones released into bloodstream; slow, long-lasting effects.

• Nervous: Electrical impulses along axons; fast, short-lived effects.

• Neuroendocrine cells: Neurons that secrete hormones.

• Exocrine glands: Secrete substances via ducts.

Feedback Mechanisms

• Negative feedback: Response reduces stimulus (e.g., insulin lowers blood glucose).

• Positive feedback: Response amplifies stimulus (e.g., childbirth).

Thermoregulation and Osmoregulation

• Thermoregulation: Maintains body temperature.

• Endotherms: Generate heat via metabolism.

• Ectotherms: Gain heat from environment.

• Osmoregulation: Controls solute concentrations and water balance.

• Excretion: Removes metabolic wastes.

• Countercurrent heat exchange: Minimizes heat loss.

• Vasodilation: Increases blood flow; Vasoconstriction: Decreases blood flow.

• Acclimatization: Physiological adjustment to environment.

• Kidney: Performs osmoregulation and excretion; basic unit is nephron.

• ADH: Increases water reabsorption in kidney.

Animal Nutrition

Dietary Requirements

• Chemical energy: Carbohydrates, proteins, lipids for ATP production.

• Organic building blocks: Carbon and nitrogen sources.

• Essential nutrients: Amino acids, fatty acids, vitamins, minerals.

Types of Diets

• Herbivores: Eat plants/algae.

• Carnivores: Eat other animals.

• Omnivores: Eat both plants and animals.

Malnutrition and Undernourishment

• Malnutrition: Lack or excess of essential nutrients.

• Undernourishment: Insufficient chemical energy; body uses stored fat, then proteins.

• Overnourishment: Excess energy intake; leads to obesity and health issues.

Food Processing Steps

• Ingestion: Eating food.

• Digestion: Mechanical and chemical breakdown.

• Absorption: Uptake of nutrients.

• Elimination: Removal of undigested material.

Digestive System Overview

• Oral cavity: Mechanical digestion, salivary enzymes.

• Stomach: Storage, churning, protein digestion (pepsin).

• Small intestine: Enzymatic hydrolysis, nutrient absorption (villi, microvilli).

• Large intestine: Water reabsorption, fermentation, feces storage.

Dietary Adaptations

• Dental: Teeth adapted for diet.

• Stomach & intestine: Carnivores have expandable stomachs; herbivores have longer alimentary canals.

• Mutualisms: Intestinal bacteria produce vitamins; ruminants have fermentation chambers.

Bioenergetics and Metabolic Rate

• Metabolic rate: Total energy used per time; measured via heat loss or O2 uptake.

• BMR: Basal metabolic rate for endotherms.

• SMR: Standard metabolic rate for ectotherms.

• Energy storage: Glycogen in liver, fat in adipose cells.

Glucose Homeostasis and Diabetes

• Blood glucose maintained at 70-110 mg/mL.

• Insulin: Lowers blood glucose.

• Glucagon: Raises blood glucose.

• Diabetes mellitus: Disrupted glucose homeostasis.

• Type 1: Autoimmune destruction of insulin-producing cells.

• Type 2: Target cells fail to respond to insulin.

Circulation and Gas Exchange

Circulatory Systems

• Open system: Hemolymph bathes organs directly; lower pressure, less energy.

• Closed system: Blood confined to vessels; higher pressure, efficient delivery.

Cardiovascular System Structure

• Arteries: Carry blood away from heart.

• Veins: Carry blood to heart.

• Capillaries: Exchange of gases and nutrients.

• Heart chambers: Atria receive blood; ventricles pump blood.

Single vs. Double Circulation

• Single: One loop; two-chambered heart (fish).

• Double: Two circuits; pulmonary and systemic (amphibians, mammals).

Cardiac Cycle and Regulation

• Systole: Contraction, pumping blood.

• Diastole: Relaxation, filling with blood.

• Valves: Prevent backflow.

• SA node: Pacemaker; AV node: Delays impulse.

Lymphatic System

• Returns fluid and proteins lost from capillaries.

• Lymph nodes filter lymph and play immune roles.

Blood Composition and Function

• Plasma: Liquid matrix; osmotic regulation, transport, defense.

• Red blood cells: Transport O2 via hemoglobin.

• White blood cells: Immune defense.

• Platelets: Clotting.

Blood Clotting and Diseases

• Coagulation: Formation of blood clots.

• Hemophilia: Lack of clotting.

• Thrombus: Clot in vessel; can cause heart attack or stroke.

• Atherosclerosis: Hardening of arteries via cholesterol deposits.

• Heart attack: Blockage of coronary arteries.

• Stroke: Blockage or rupture of brain arteries.

• LDL: Delivers cholesterol; HDL: Removes excess cholesterol.

• Hypertension: High blood pressure; risk factor for heart disease.

Gas Exchange and Respiratory Systems

• Diffusion: Moves gases over short distances.

• Partial pressure: Determines direction of gas movement.

• Respiratory surfaces: Must be moist, large, and thin.

• Gills: Outfoldings for aquatic gas exchange; use countercurrent exchange.

• Tracheal systems: Air tubes in insects; direct gas exchange.

• Lungs: Infoldings for terrestrial gas exchange; alveoli are sites of exchange.

• Breathing: Negative pressure draws air in; controlled by medulla oblongata.

• Respiratory pigments: Hemoglobin (vertebrates), hemocyanin (arthropods/molluscs).

Equation for partial pressure:

Example: Countercurrent exchange in fish gills maximizes O2 uptake.

Additional info: Academic context and expanded explanations were added to ensure completeness and clarity for exam preparation.