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AP Biology

This article discusses the process of plant reproduction, including pollination, double fertilization, and seed development. It also covers the role of plant hormones in regulating growth and development.

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AP Biology

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  1. AP Biology Exam Critical Concepts Diversity and Homeostasis Chapters 38,39,43,45,48

  2. Chapter 38 Plant reproduction Carpel Stigma Anther Stamen Style Ovary Filament Sepal Petal Receptacle

  3. Chapter 38 Plant reproduction cont. • Flowers: reproductive shoots of plants • Receptacle: attaches flower to the stem • Flowers consist of four floral organs: • Sepals: leaf like cover to flower bud • Petals: Attracts insects • Stamens: Male reproduce structures consists of Filament is a stalk topped by an anther with • Carpels: Female reproductive structures made of Style holds up a stigma on which pollen lands ovary at base containing one or more ovules pistil a group of fused carpels

  4. Chapter 38 Plant reproduction cont. • Pollination: transfer of pollen from an anther to a stigma • can be by wind, water, bee, moth and butterfly, fly, bird, bat, or water • Pollen develops from microspores within the microsporangia, or pollen sacs of anthers • Pollen grain produces a pollen tube that grows down into the ovary and discharges sperm near the embryo sac • Within an ovule, megaspores are produced by meiosis and develop into embryo sacs

  5. Chapter 38 Plant reproduction cont. • After landing on a stigma, a pollen grain produces a pollen tube that extends between the cells of the style toward the ovary • Double fertilization results from the discharge of two sperm from the pollen tube into the embryo sac • One sperm fertilizes the egg, and the other combines with the polar nuclei, giving rise to the triploid (3n) food-storing endosperm

  6. Chapter 38 Plant reproduction cont. • After double fertilization, each ovule develops into a seed • The ovary develops into a fruit enclosing the seed(s)

  7. Chapter 38 Plant reproduction cont. • Pollination: the transfer of pollen from an anther to a stigma • can be by wind, water, bee, moth and butterfly, fly, bird, bat, or water • Pollen tube: After landing on a stigma, a pollen grain produces a tube which extends between the cells of the style toward the ovary • Double fertilization: the discharge of two sperm from the pollen tube into the embryo sac • One sperm fertilizes the egg • other combines with the polar nuclei, giving rise to the triploid (3n) food-storing endosperm

  8. Chapter 38 Plant reproduction cont. • After double fertilization, each ovule develops into a seed • The ovary develops into a fruit enclosing the seed(s) • Endosperm development usually precedes embryo development • Monocots and some eudicots: endosperm stores nutrients that can be used by the seedling • Eudicots: food reserves of the endosperm are exported to the cotyledons • Seed coat: food supply are enclosed by a hard protective covering

  9. Chapter 38 Plant reproduction cont. • Seed dormancy: increases the chances that germination will occur at a time and place most advantageous to the seedling • breaking of seed dormancy often requires environmental cues, such as temperature or lighting changes • Imbibition: uptake of water due to low water potential of the dry seed breaks dormancy • The radicle (embryonic root) emerges first • Next, the shoot tip breaks through the soil surface

  10. Chapter 38 Plant reproduction cont. • Fruit: develops from the ovary • protects the enclosed seeds • aids in seed dispersal by wind or animals • Classified as: • Dry: the ovary dries out at maturity • Fleshy: the ovary becomes thick, soft, and sweet at maturity • Fruits are also classified by their development: • Simple: single or several fused carpels • Aggregate: single flower with multiple separate carpels • Multiple: group of flowers called an inflorescence

  11. Chapter 38 Plant reproduction cont. • Fruit dispersal mechanisms include: • Water • Wind • Animals • Genetically modified plants may increase the quality and quantity of food worldwide • Transgenic crops have been developed that: • Produce proteins to defend them against insect pests • Tolerate herbicides • Resist specific diseases

  12. Chapter 39 Plant Hormones • Signaling in plants follow the basic steps as all cellular responses: • Reception: plants have cellular receptors that detect changes in their environment • For a stimulus to elicit a response, certain cells must have an appropriate receptor • Transduction: stimulation of the receptor initiates a specific signal transduction pathway • Response: regulation of cellular activity

  13. Chapter 39 Plant Hormones cont. • Hormones: chemical signals that coordinate different parts of an organism • control plant growth and development by affecting the division, elongation, and differentiation of cells • produced in very low concentration, but a minute amount can greatly affect growth and development of a plant organ • Tropism: any response resulting in curvature of organs toward or away from a stimulus is called a often caused by hormones

  14. Chapter 39 Plant Hormones cont. • Auxin: One of the most common plant hormone • Promotes elongation of coleoptiles • Auxin transporter proteins move the hormone from the basal end of one cell into the apical end of the neighboring cell • Involved in root formation and branching • stimulates proton pumps in the plasma membrane • Expansins: lower the pH in the cell wall, activating, enzymes that loosen the wall’s fabric • With the cellulose loosened, the cell can elongate

  15. Chapter 39 Plant Hormones cont. • Cytokines: named because they stimulate cytokinesis • produced in actively growing tissues such as roots, embryos, and fruits • work together with auxin to control cell division and differentiation • Cytokinins, auxin, and other factors interact in the control of apical dominance, a terminal bud’s ability to suppress development of axillary buds • If the terminal bud is removed, plants become bushier

  16. Chapter 39 Plant Hormones cont. • Gibberellins: have a variety of effects, • stimulate cell elongation and cell division in stems • in many plants, both auxin and gibberellins must be present for fruit to set • are used in spraying of Thompson seedless grapes ( so they a seedless) • after water is imbibed, release of gibberellins from the embryo signals seeds to germinate

  17. Chapter 39 Plant Hormones cont. • Brassinosteroids: are chemically similar to the sex hormones of animals • induce cell elongation and division in stem segments • Abscisic Acid (ABA): slows growth • Causes Seed dormancy • Seed dormancy ensures that the seed will germinate only in optimal conditions • In some seeds, dormancy is broken when ABA is removed by heavy rain, light, or prolonged cold • primary internal signal that enables plants to withstand drought

  18. Chapter 39 Plant Hormones cont. • Ethylene: Hormone produced in response to stresses such as drought, flooding, mechanical pressure, injury, and infection • Effects include response to mechanical stress, leaf abscission, and fruit ripening • Ethylene induces the triple response, which allows a growing shoot to avoid obstacles • Senescence: programmed death of plant cells or organs • Apoptosis: programmed destruction of cells, organs, or whole plants • Leaf Abscission: Causes leaf drop

  19. Chapter 39 Plant Hormones cont. • Light cues many key events in plant growth and development • Photomorphogenesis: effects of light on plant morphology • Plants detect not only presence of light but also its direction, intensity, and wavelength (color) • Action spectrum depicts relative response of a process to different wavelengths

  20. Chapter 39 Plant Hormones cont. • Circadian Rhythm: cycles that are about 24 hours long and are governed by an internal “clock” • can be entrained to exactly 24 hours by the day/night cycle • The clock may depend on synthesis of a protein regulated through feedback control and may be common to all eukaryotes • Photoperiod: the relative lengths of night and day, is the environmental stimulus plants use most often to detect the time of year • Photoperiodism: physiological response to photoperiod

  21. Chapter 39 Plant Hormones cont. • Herbivory: animals eating plants • a stress that plants face in any ecosystem • Plants counter excessive herbivory with physical defenses such as thorns and chemical defenses such as distasteful or toxic compounds • Some plants even “recruit” predatory animals that help defend against specific herbivores • Plants damaged by insects can release volatile chemicals to warn other plants of the same species

  22. Chapter 43 Immunity • Acquired immunity, or adaptive immunity, develops after exposure to agents • Innate immunity: present before any exposure • effective from the time of birth is nonspecific • consists of external barriers plus internal cellular and chemical defenses • Barriers: include the skin and mucous membranes of the respiratory, urinary, and reproductive tracts • Mucus traps and allows for the removal of microbes • fluids including saliva, mucus, and tears are hostile to microbes • The low pH of skin and the digestive system prevents growth of microbes

  23. Chapter 43 Immunity cont. • White Blood cells: engulf pathogens in the body then fuses with a lysosome to destroy the microbe • types of phagocytic cells: • Neutrophils engulf and destroy microbes • Macrophages are part of the lymphatic system and are found throughout the body • Eosinophils discharge destructive enzymes • Dendritic cells stimulate development of acquired immunity

  24. Chapter 43 Immunity cont. • Inflammatory response : Following an injury, mast cells release histamine,which promotes changes in blood vessels • These changes increase local blood supply and allow more phagocytes and antimicrobial proteins to enter tissues • Pus, a fluid rich in white blood cells, dead microbes, and cell debris, accumulates at the site of inflammation • can be either local or systemic (throughout the body)

  25. Chapter 43 Immunity cont. • Fever: a systemic inflammatory response triggered by pyrogens released by macrophages, and toxins from pathogens • Septic shock: a life-threatening condition caused by an overwhelming inflammatory response • Natural killer (NK) cells: Attack Cancerous or infected cells that on longer express the protein, MHC protein on their surface

  26. Chapter 43 Immunity cont. • Acquired immunity: Immunity from infection or exposure to the pathogen • Lymphocytes or White blood cells: recognize and respond to antigens, foreign molecules • Lymphocytes that mature in the thymus are called T cells,and those that mature in bone marrow are called B cells • Lymphocytes contribute to immunological memory • Cytokines:secreted by macrophages and dendritic cells to recruit and activate lymphocytes

  27. Chapter 43 Immunity cont. • Antigen: any foreign molecule to which a lymphocyte responds • A single B cell or T cell has about 100,000 identical antigen receptors • The first exposure to a specific antigen represents the primary immune response • During this time, effector B cells called plasma cells are generated, and T cells are activated to their effector forms • In the secondary immune response, memory cells facilitate a faster, more efficient response

  28. Chapter 43 Immunity cont. • Active immunity: develops naturally in response to an infection • can also develop following immunization, also called vaccination • In immunization, a nonpathogenic form of a microbe or part of a microbe elicits an immune response to an immunological memory

  29. Chapter 43 Immunity cont. • Passive immunity: provides immediate, short-term protection that is conferred naturally when IgG crosses the placenta from mother to fetus or when IgA passes from mother to infant in breast milk • It can be conferred artificially by injecting antibodies into a nonimmune person

  30. Chapter 43 Immunity cont. • MHC molecules: different among genetically nonidentical individuals • Differences in MHC molecules stimulate rejection of tissue grafts and organ transplants • Immunosuppressive drugs facilitate transplantation • Lymphocytes in bone marrow transplants may cause the donor tissue to reject the recipient • Allergies: exaggerated (hypersensitive) responses to antigens called allergens • allergies such as hay fever, IgE antibodies produced after first exposure to an allergen attach to receptors on mast cells

  31. Chapter 43 Immunity cont. • The next time the allergen enters the body, it binds to mast cell–associated IgE molecules • Mast cells release histamine and other mediators that cause vascular changes leading to typical allergy symptoms • An acute allergic response can lead to anaphylactic shock, a life-threatening reaction that can occur within seconds of allergen exposure

  32. Chapter 43 Immunity cont. • Autoimmune diseases: the immune system loses tolerance for self and turns against certain molecules of the body • diseases include • systemic lupus • rheumatoid arthritis • diabetes mellitus • multiple sclerosis • Some viruses may remain in a host in an inactive state called latency • Herpes simplex viruses can be present in a human host without causing symptoms

  33. Chapter 43 Immunity cont. • The frequency of certain cancers increases when the immune response is impaired • Two suggested explanations are • Immune system normally suppresses cancerous cells • Increased inflammation increases the risk of cancer

  34. Chapter 45 Hormones and Animals • Communication in animals include: • Endocrine system: secretes hormones that coordinate slower but longer-acting responses including reproduction, development, energy metabolism, growth, and behavior • Chemical signals bind to receptor proteins on target cells • Only target cells respond to the signal • Nervous system: conveys high-speed electrical signals along specialized cells called neurons; these signals regulate other cells

  35. Chapter 45 Hormones and Animals cont. • Hormones: Chemical secreted into extracellular fluids and travel via the bloodstream • mediate responses to environmental stimuli and regulate growth, development, and reproduction • Endocrine glands: ductless and secrete hormones directly into surrounding fluid • Local Regulators: are chemical signals that travel over short distances by diffusion • regulate blood pressure, nervous system function, and reproduction, divided into two types • Paracrine: act on cells near the secreting cell • Autocrine: act on the secreting cell itself

  36. Chapter 45 Hormones and Animals cont. • Neurotransmitters: secreted chemical signals that diffuse a short distance to bind to receptors and play a role in sensation, memory, cognition, and movement • Neurohormones: a class of hormones that originate from neurons in the brain and diffuse through the bloodstream

  37. Chapter 45 Hormones and Animals cont. • Pheromones: are chemical signals that are released from the body and used to communicate with other individuals in the species • mark trails to food sources, warn of predators, and attract potential mates • Three major classes of molecules function as hormones in vertebrates: • Polypeptides (proteins and peptides) • Amines derived from amino acids • Steroid hormones

  38. Chapter 45 Hormones and Animals cont. • Epinephrine: a hormone that has multiple effects in mediating the body’s response to short-term stress • binds to receptors on the plasma membrane of liver cells • This triggers the release of messenger molecules that activate enzymes and result in the release of glucose into the bloodstream

  39. Chapter 45 Hormones and Animals cont. • The same hormone may have different effects on target cells that have: • Different receptors for the hormone • Different signal transduction pathways • Different proteins for carrying out the response • A hormone can also have different effects in different species

  40. Chapter 45 Hormones and Animals cont. • Types of local regulators: • Cytokines and growth factors • Nitric oxide (NO) • Prostaglandins: help regulate aggregation of platelets, an early step in formation of blood clots • Negative Feedback: inhibits a response by reducing the initial stimulus • regulates many hormonal pathways involved in homeostasis

  41. Chapter 45 Hormones and Animals cont. • Control of blood sugar: A case study in Homeostasis: • Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis • The pancreas has clusters of endocrine cells called islets of Langerhans • Alpha cells: produce glucagon • Betacells: produce insulin • Insulin: reduces blood glucose levels by: • Promoting the cellular uptake of glucose • Slowing glycogen breakdown in the liver • Promoting fat storage

  42. Chapter 45 Hormones and Animals cont. • Glucagon:increases blood glucose levels by • Stimulating conversion of glycogen to glucose in the liver • Stimulating breakdown of fat and protein into glucose • Diabetes Mellitus: is perhaps the best-known endocrine disorder • caused by a deficiency of insulin or a decreased response to insulin in target tissues • marked by elevated blood glucose levels

  43. Chapter 45 Hormones and Animals cont. • Type I (insulin-dependent): is an autoimmune disorder in which the immune system destroys pancreatic beta cells • Type II (non-insulin-dependent): involves insulin deficiency or reduced response of target cells due to change in insulin receptors

  44. Chapter 48 Neurons • Neurons: nerve cells that transfer information within the body • Two types of signals to communicate: • Electrical signals (long-distance) • Chemical signals (short-distance) • Ganglia: simple clusters of neurons • Brain: more complex organization of neurons • Process information with three stages or types: • sensory neurons: detect external stimuli • Interneurons : integrate the information • motor neurons: trigger muscle or gland activity

  45. Chapter 48 Neurons cont. • Many animals have a complex nervous system which consists of: • A central nervous system (CNS) where integration takes place; this includes the brain and a nerve cord • A peripheral nervous system (PNS), which brings information into and out of the CNS • Most of a neuron’s organelles are in the cell body • Most neurons have dendrites, highly branched extensions that receive signals from other neurons • The axon is typically a much longer extension that transmits signals to other cells at synapses

  46. Chapter 48 Neurons cont. • Synapse: junction between an axon and another cell • Synaptic terminal: one axon passes information across the synapse in the form of chemical messengers called neurotransmitters • Most neurons are nourished or insulated by cells called glia

  47. Chapter 48 Neurons cont. • Membrane potential: difference in electrical charge across its plasma membrane • Messages are transmitted as changes in membrane potential • Resting potential: the membrane potential of a neuron not sending signals • The concentration of K+ is greater inside the cell, while the concentration of Na+ is greater outside the cell • Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane

  48. Chapter 48 Neurons cont. • The opening of ion channels in the plasma membrane converts chemical potential to electrical potential • A neuron at resting potential contains many open K+ channels and fewer open Na+ channels; K+ diffuses out of the cell • Anions trapped inside the cell contribute to the negative charge within the neuron • In a resting neuron, the currents of K+ and Na+ are equal and opposite, and the resting potential across the membrane remains steady

  49. Chapter 48 Neurons cont. • The speed of an action potential increases with the axon’s diameter • Myelinsheath: insulated axons which causes an action potential’s speed to increase • Neurotransmitters: Chemical signal across the synapse • can produce different effects in different types of cells • There are five major classes of neurotransmitters: acetylcholine, biogenic amines, amino acids, neuropeptides, and gases

  50. Chapter 48 Neurons cont. • Acetylcholine: common neurotransmitter in vertebrates and invertebrates • it is usually an excitatory transmitter • Biogenic amines: These neurotransmitters include: • Epinephrine • Norepinephrine • Opamine • serotonin • They are active in the CNS and PNS • Gas Neurotransmitters: nitric oxide and carbon monoxide are local regulators in the PNS

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