Land plants alternate between a haploid gametophyte and a diploid sporophyte. The generations need not be equal in size or duration. Animals typically have a diploid multicellular stage; fungi and protists have diverse life cycles, and some algae also show alternation of generations.

The four pairs are correctly matched. Ethylene promotes fruit ripening; gibberellins promote stem elongation and flowering in some plants; auxin contributes to shoot phototropism; and abscisic acid promotes seed dormancy and inhibits growth.

A stoma is a pore whose opening is regulated by two guard cells. Phloem transports sugars and other organic solutes, whereas xylem transports water and minerals. The cuticle is a waxy protective layer secreted by epidermal cells.

Both angiosperms and gymnosperms are seed plants contained in vascular plants. Flowering plants and producing fruit are characteristics of angiosperms. Naked seeds are characteristics of gymnosperms.

Mycorrhizae are associations between fungal hyphae and plant roots. In a typical mutualistic association, the plant supplies organic carbon and the fungus improves water and mineral uptake, including phosphate uptake. Fungi do not have true roots.

Autotrophs use inorganic carbon, usually CO2, to make organic compounds. Some archaea obtain energy by oxidizing reduced sulfur compounds and fix CO2. Photosynthetic protists and most plants are autotrophs, and bacteria include photoautotrophs and chemoautotrophs. Fungi obtain organic carbon from other organisms.

A radula is a toothed feeding structure used by many snails to scrape or cut food. In many shelled gastropods, an operculum closes the shell opening. Siphons direct water flow, adductor muscles close bivalve shells, and the mantle covers the visceral mass and secretes the shell.

The three domains are Archaea, Bacteria, and Eukarya.

Zygotes, sporophytes, and sporangia are diploid, whereas spores, gametophytes, and gametes are haploid.

The oomycete Phytophthora infestans causes potato late blight. Oomycetes grow as absorptive hyphae resembling those of fungi, but their cell walls contain cellulose rather than the chitin characteristic of fungi. Oomycetes include water molds and downy mildews.

Pits permit water movement between xylem conducting cells. Sieve-tube elements and companion cells belong to phloem. Transpiration-driven tension, together with water cohesion, moves water through xylem. Pith lies inside the vascular tissue in typical eudicot stems. During secondary growth, periderm replaces the epidermis; it includes cork, cork cambium, and phelloderm.

For the listed groups, the order is jawless fishes (2), bony fishes (3), reptiles (4), and birds (1). This is a sequence of first appearances, not a claim that living groups form a single ancestor-to-descendant chain. Birds arose within the reptile lineage.

Typical monocots have one cotyledon, fibrous roots, parallel leaf veins, and scattered stem vascular bundles. They usually lack the vascular cambium responsible for conventional secondary growth. Some monocots can thicken by other mechanisms.

Correct order of hierarchy from high to low:

Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species

Arthropods have jointed appendages, a chitin-containing exoskeleton, and an open circulatory system. Many have well-developed sensory structures and undergo metamorphosis. A closed circulatory system is not a typical arthropod feature.

Oviparity means laying eggs that develop outside the parent. It does not by itself specify whether fertilization occurred. Parthenogenesis is development from an unfertilized egg; budding and fragmentation can produce offspring asexually, with regeneration restoring missing structures.

Basidiomycota produce sexual spores on basidia. Many form basidiocarps, including mushrooms and puffballs; rusts also belong to this phylum but have different reproductive structures.

Species is the most specific rank listed. The standard hierarchy runs from domain through kingdom, phylum, class, order, family, and genus to species.

Traditional kingdom Protista groups diverse eukaryotes, including euglenids, many algae, amoebae, and ciliates. Most are unicellular, but some algae are multicellular. Modern classifications distribute these organisms among several evolutionary lineages.

In the typical deuterostome pattern, the blastopore becomes the anus and the mouth forms later at a different site. In the typical protostome pattern, the mouth forms at or near the blastopore.

The notochord is a flexible support rod located between the dorsal nerve cord and the digestive tract. It provides support and muscle attachment during development. In most vertebrates, the vertebral column largely replaces it, although remnants may persist.

A potato is a stem tuber. Rhizomes are horizontal underground stems, as in ginger. Stolons are horizontal stems that can produce new plants, as in strawberries. Bulbs, such as onions, have a short stem surrounded by fleshy storage leaves. Cork cambium produces secondary protective tissue.

Cnidocytes are characteristic of cnidarians, such as Hydra. Sponges use choanocytes to help create water currents and capture suspended food.

Fission divides one individual into two. Parthenogenesis is development from an unfertilized egg. Regeneration restores lost body parts; after fragmentation, suitable body pieces can regenerate into new individuals. Hermaphrodites have both male and female reproductive systems.

Collenchyma cells remain alive at maturity and have unevenly thickened primary walls. Many sclerenchyma cells are dead at maturity and have thick, lignified secondary walls. Thus, the claim that both cell types are dead is incorrect.

Mosses are bryophytes, which are nonvascular plants.

Insects, such as grasshoppers, use tracheae for gas exchange and Malpighian tubules for excretion. Earthworms use metanephridia for excretion. Sponge choanocytes help create water currents and capture suspended food.

Photoautotrophs use light for energy and inorganic carbon, usually CO2. Photoheterotrophs use light for energy and organic carbon. Chemoautotrophs obtain energy from chemical reactions and use inorganic carbon. Chemoheterotrophs, including animals and fungi, obtain energy and carbon from organic compounds. Heteroautotrophy is not one of these four standard categories.

The traditional five kingdoms are Monera, Protista, Fungi, Plantae, and Animalia. Eukarya is a domain, Chordata is a phylum, Mammalia is a class, and Homo sapiens is a species.

Cnidarians have a gastrovascular cavity, tentacles bearing cnidocytes, and two main germ layers. Many have polyp and medusa forms, but some, including Hydra and corals, lack a medusa stage. Jellyfish, corals, and sea anemones all belong to Cnidaria. Triploblasty is the incorrect feature.

Diplomonads and parabasalids have highly modified mitochondria. Oomycete hyphae resemble fungal hyphae but evolved independently. Photosynthetic euglenids have plastids surrounded by three membranes, consistent with secondary endosymbiosis involving a green alga. Lichens associate a fungus with a photosynthetic partner, usually an alga or a cyanobacterium. Thus, none of A–D is incorrect.

Fertilization produces a diploid zygote, the first cell of the sporophyte generation. The zygote divides by mitosis to form the multicellular sporophyte. Meiosis in the sporophyte produces haploid spores, which develop into gametophytes.

Earthworms are annelids. Their metanephridia remove nitrogenous wastes and help regulate water and salts. Mollusks also have metanephridial organs, so metanephridia alone do not uniquely identify Annelida. In insects, Malpighian tubules transfer wastes from hemolymph into the gut.

Most mammals are viviparous: young develop inside the mother and receive maternal nourishment, typically through a placenta. In ovoviviparity, eggs remain inside the parent and embryos depend on yolk. Oviparous animals lay eggs that develop outside the parent. Reptiles include more than one of these reproductive modes.

Domain is the broadest rank listed. Each domain contains many lower-ranking taxa.

In the traditional five-kingdom system, Monera includes prokaryotes, not viruses. Prokaryotes have a nucleoid; protists are eukaryotes with a nucleus. Prokaryotes commonly reproduce by binary fission, and some have motility structures. Plantae and Protista include photosynthetic organisms; photosynthetic bacteria also exist. Statements III and IV are correct.

Traditional kingdom Monera groups prokaryotes. Modern classifications separate them into domains Bacteria and Archaea. Protista, Fungi, Plantae, and Animalia contain eukaryotes.

Microspores develop into male gametophytes. Megaspores develop into female gametophytes. Archegonia produce eggs in plants that have these structures, and antheridia produce sperm in plants that have them. Zygotes and sporophytes are diploid stages shared by the life cycle.

Echinoderms and chordates are deuterostomes. Echinoderms are more closely related to hemichordates within Ambulacraria. Echinoderm larvae are bilateral, whereas adults typically have pentaradial symmetry. Their water vascular system operates tube feet, and their internal skeleton contains calcareous ossicles. All statements A–D are correct.

Fungi include molds, yeasts, and mushrooms. They are heterotrophs; different species act as decomposers, parasites, or mutualists.

Protists are eukaryotes with membrane-bound nuclei, whereas organisms traditionally placed in Monera are prokaryotes with nucleoids. Both groups include organisms that divide by binary fission and organisms that obtain organic carbon from other organisms.

Clams belong to phylum Mollusca. Crabs, shrimp, grasshoppers, and ticks belong to phylum Arthropoda.

Brown algae are multicellular algae, often marine. They include kelps such as Laminaria and Macrocystis.

Land plants share their closest algal ancestry with charophytes within the green algal lineage. Shared traits include chlorophylls a and b and related chloroplast features. The other listed groups are more distantly related to land plants.

Traditional kingdom Monera groups prokaryotes. Binary fission increases cell number, whereas conjugation transfers DNA between cells. These processes are not exclusive to Monera: some protists, including ciliates, also undergo binary fission and conjugation. The prokaryotic condition distinguishes the answer here.

Most fungi grow as networks of hyphae called mycelia, although yeasts are unicellular. Fungi secrete enzymes that digest organic material outside their bodies and then absorb the products. Many reproduce both sexually and asexually, and some form symbiotic associations.

Ascomycota are sac fungi. Their sexual spores, called ascospores, form inside sacs called asci; many also produce asexual spores called conidia. Many lichen-forming fungi are ascomycetes. Arbuscular mycorrhizal fungi are traditionally placed in Glomeromycota.

Gymnosperms, including pines, ginkgo, and cycads, bear seeds that are not enclosed in an ovary. Mosses and hornworts are nonvascular, gametophyte-dominant plants. Bananas and apples are angiosperms, which produce flowers and fruits.

Gastropods, including snails and slugs, undergo torsion during development and have an open circulatory system. Many have a radula, and some shelled species have an operculum. Cephalopods have highly developed heads and a closed circulatory system. Siphons occur in several molluscan groups, including bivalves and cephalopods.

Vascular plants are divided into seedless vascular plants and seed plants. Lycophytes, such as club mosses and spike mosses, and pterophytes, such as ferns and horsetails, are included in seedless vascular plants. Gymnosperms, such as pines and ginkgos, and angiosperms, such as maples and bananas, are included in seed plants. Hornworts are bryophytes.

Chordata is characterized by a notochord and a dorsal hollow nerve cord, along with other chordate features, at some stage of development. Animal phyla form branching evolutionary lineages; they cannot be ranked as a single sequence from least to most developed.

An earthworm is an annelid with bilateral symmetry, a true coelom, a ventral nerve cord, and a complete digestive tract with a mouth and anus. Its metanephridia handle nitrogenous wastes and water balance; respiratory CO2 diffuses across the body surface.

Flatworms are triploblastic acoelomates: they lack a body cavity between the gut and body wall. They include free-living species and parasitic flukes and tapeworms. Traditional groups include Turbellaria, Trematoda, and Cestoda, although modern classifications revise these groupings.

A stamen consists of an anther and a filament. A carpel includes a stigma, style, and ovary. Sepals are leaflike structures that typically surround the base of a flower.

Nematodes and rotifers are triploblastic animals with a digestive tract and a pseudocoel. A pseudocoel is a body cavity that is not completely lined by mesoderm. It is not a partly formed cavity.

Classic chordate features include a notochord, a dorsal hollow nerve cord, pharyngeal slits or pouches, and a post-anal tail. Some features also occur in other lineages, but their combination characterizes chordates. A ventral nerve cord is not a classic chordate feature.

Traditional Monera groups prokaryotes. Gram-positive bacteria, cyanobacteria (formerly called blue-green algae), and spirochetes are bacteria. Sulfolobus is an archaeon. Amoebae are eukaryotes traditionally placed in Protista.

Plasmodium has a complex life cycle involving humans and mosquitoes. In humans, it first infects liver cells and then red blood cells. Sexual reproduction occurs in the mosquito.

Fungi break down dead organisms and absorb nutrients.

The stigma receives pollen during pollination. A pollen tube can then grow through the style toward an ovule in the ovary. Fertilization occurs when sperm unite with cells of the female gametophyte. Anthers produce pollen, and petals often attract animal pollinators.

Nematodes are unsegmented roundworms with a complete digestive tract, a cuticle, longitudinal body-wall muscles, and a pseudocoel that is not completely lined by mesoderm. Some, including Ascaris and hookworms, are parasitic; many others are free-living.

Classes Cephalopoda, Bivalvia, and Gastropoda belong to Mollusca, a protostome phylum. Crustaceans belong to phylum Arthropoda.

The mantle covers the visceral mass and typically secretes the shell. Most mollusks have an open circulatory system, but cephalopods have a closed system. Strong adductor muscles close the shells of bivalves.

An octopus is a cephalopod mollusk with a complex central nervous system and well-developed eyes. The other listed invertebrates have different nervous system organizations. A dog is a vertebrate. These differences do not rank living organisms along an evolutionary ladder.

Nematodes and rotifers have a pseudocoel, a body cavity that is not completely lined by mesoderm. They are triploblastic and bilaterally symmetrical and typically have a complete digestive tract with a mouth and anus.

Chordata includes Vertebrata and two invertebrate groups: Cephalochordata (lancelets) and Urochordata, also called Tunicata (tunicates). Chordates are deuterostomes and have a notochord at some stage. Sea stars belong to Echinodermata.

Insects are arthropods with three main body regions—head, thorax, and abdomen—and three pairs of thoracic legs. Many adults have two pairs of wings, but some have one pair or none. Insects generally use tracheae for gas exchange and Malpighian tubules for excretion.