AP Biology

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