BIOLOGY: CHAPTER 13

Which is the only animal phylum to have over 1 million described species? flatworms chordates mollusks arthropods nematodes

arthropods

In order to be classified as an animal, an organism must be motile at some stage in their life cycle, consume other organisms for energy, and: be multicellular. perform photosynthesis. reproduce sexually. have a spinal cord. develop their gut from back to front.

be multicellular.

Which insect order has roughly six times as many named species as all birds, mammals, fish, amphibians, and reptiles combined? bees, wasps, ants, and sawflies flies beetles butterflies and moths grasshoppers and crickets

beetles

Birds are grouped with turtles, lizards, snakes, alligators, and crocodiles. Birds, however, have feathers and can generate their own body heat, which other reptiles cannot do. Which likely explains the original evolutionary function of feathers in early reptiles? structural support insulation locomotion flight behavioral displays

behavioral displays

Which characteristics define an arthropod? lacks tissues, gut develops from back to front, and radial symmetry defined tissues, gut develops from back to front, and bilateral symmetry defined tissues, radial symmetry, and gut develops from front to back lacks tissues, gut develops from front to back, and grows by adding continuously to its body bilateral symmetry, gut develops from front to back, and grows by molting

bilateral symmetry, gut develops from front to back, and grows by molting

Both birds and mammals have four-chambered hearts. But birds are more closely related to crocodiles, which have three-chambered hearts, than they are to mammals. The correct interpretation of these observations is that: birds and mammals evolved four-chambered hearts independently. the trend in heart evolution is from four-chambered to three-chambered. having a four-chambered heart would be detrimental to crocodiles. the number of heart chambers that an organism possesses can never be an indication of evolutionary relationships. crocodiles evolved from a group that originally had four-chambered hearts.

birds and mammals evolved four-chambered hearts independently.

Both birds and mammals have four-chambered hearts. But birds are more closely related to crocodiles, which have three-chambered hearts, than they are to mammals. The correct interpretation of these observations is that: the trend in heart evolution is from four-chambered to three-chambered. having a four-chambered heart would be detrimental to crocodiles. crocodiles evolved from a group that originally had four-chambered hearts. birds and mammals evolved four-chambered hearts independently. the number of heart chambers that an organism possesses can never be an indication of evolutionary relationships.

birds and mammals evolved four-chambered hearts independently.

The notochord that characterizes all chordates at some stage in their life cycle provides all of the following functions except: a longitudinal stiffening of the main body axis. makes locomotion possible by stiffening when muscles contract. bony protection for the nerve cord. a base for trunk muscles. an axis around which the vertebral column develops.

bony protection for the nerve cord.

What is the relationship between coral and zooxanthellae? Competitive; zooxanthellae are a type of algae that compete with coral for space and nutrients. There is no relationship between the two. Zooxanthellae are terrestrial animals, and coral is aquatic. Commensal; zooxanthellae are a type of algae that resides among the coral, but the coral is unaffected by its presence. Mutually symbiotic; zooxanthellae provide the coral with nutrition, while the coral provide zooxanthellae with carbon dioxide. Parasitic; zooxanthellae are a type of algae that grows inside coral, feeding off of the coral's nutrients and causing coral bleaching over time.

Mutually symbiotic; zooxanthellae provide the coral with nutrition, while the coral provide zooxanthellae with carbon dioxide.

Humans are not a part of which taxonomic group? apes animals primates Old World monkeys placental mammals

Old World monkeys

In order to build coral reefs, which are home to the most diverse marine ecosystems on the planet, corals secrete: hydrogen ions. potassium phosphate. calcium phosphate. calcium carbonate. cnidocytes.

calcium carbonate.

The development of jaws allowed fishes to: withstand the pull of gravity. capture and kill prey. acquire dissolved oxygen from water. float in water. control their movement in water.

capture and kill prey.

Cephalopods include all of these kinds of animals except: clams. squid. cuttlefish. octopuses. nautiluses.

clams.

All cnidarians have tentacles that are armed with rows of stinging: cilia. polyps. cnidocytes. flagella. collar cells.

cnidocytes.

Nearly one-third of amphibian populations are facing extinction. Which factor does NOT attribute to the universal decline in amphibian populations? climate change competition from mammals habitat destruction fungal disease pollution

competition from mammals

Which characteristic could NOT be used to differentiate the three worm phyla, Annelida, Platyhelminthes, and Nematoda? bilateral symmetry growth by molting the presence of eyespots presence of a complete gut, with two openings segmentation

bilateral symmetry

Which characteristics are found in all chordates? radial symmetry, defined tissues, and gut develops from front to back bilateral symmetry, defined tissues, and gut develops from back to front bilateral symmetry, defined tissues, and gut develops from front to back radial symmetry, gut develops from front to back, and grows by molting asymmetrical, gut develops from front to back, and lacks tissues

bilateral symmetry, defined tissues, and gut develops from back to front

Three major differences between humans and chimpanzees are that humans are bipedal, have a larger brain, and have a larger body. Which of these characteristics evolved first? bipedality and larger brain together larger brain, bipedality, and larger body at the same time larger brain larger body bipedality

bipedality

You are eating in a French restaurant, and you read that snails are on the menu. Being a knowledgeable biologist, you inform the other members at the table that this restaurant is serving: nautiluses. annelids. cephalopods. gastropods. bivalves.

gastropods.

Birds are a branch of the reptile lineage but, unlike other reptiles, birds are able to: have multiple offspring at the same time control their body temperature using external heat produce milk for their young produce amniotic eggs generate body heat

generate body heat

Which animal is not a chordate? lancelet lizard frog grasshopper fish

grasshopper

An air environment, gravity, and desiccation are three challenges that were addressed in the evolution of reptiles. What three evolutionary innovations addressed these challenges? dorsal nerve cord, notochord, and a post-anal tail better limb support, gills, and pharyngeal slits lungs, better limb support, and the amniotic egg gills, bony skeleton, and lungs the amniotic egg, sturdy fins, and a cartilaginous skeleton

lungs, better limb support, and the amniotic egg

Which characteristic is common to all mammals? viviparity teeth bipedal land-dwelling mammary glands

mammary glands

Sponges are not: hermaphrodites. members of phylum Porifera. sessile. medusa. able to reproduce asexually.

medusa.

Some insects have a life history that is divided into two or three unique stages known as _____, during which their bodies undergo distinct changes. metamorphosis mutation transformation pupation sessile

metamorphosis

Collar cells are found in: flatworms. shrimp. segmented worms. clams. sponges.

sponges.

Which of these is not an echinoderm? barnacles sea urchins sea stars sand dollars sea cucumbers

barnacles

Octopuses belong to which group? crustaceans gastropods cephalopods cnidarians arachnids

cephalopods

Trichinella worms sometimes cause the disease known as trichinosis in humans when undercooked pork is eaten. These organisms have long cylindrical bodies but no segmentation. This species is most similar to which animal? jellyfish flatworms earthworms Portuguese man-o'-war nematodes

nematodes

Marsupials are thought to be most closely related to: placental mammals. amphibians. reptiles. monotremes. birds.

placental mammals.

The tissues of most shallow-water corals harbor photosynthetic algae called: medusae. cnidocytes. cyanobacteria. nematocysts. zooxanthellae.

zooxanthellae.

Crabs, lobsters, and barnacles all belong to which group? mollusks crustaceans cephalopods gastropods arachnids

crustaceans

Which types of arthropods are not primarily land-dwelling? arachnids millipedes crustaceans insects centipedes

crustaceans

What group of animals does recent DNA evidence suggest may have been the first group to diverge from the rest of the animals? sponges cnidarians ctenophores chordates flatworms

ctenophores

Animals such as jellyfish and cnidarians acquire nutrients and oxygen by: using a trachea system. direct diffusion. breathing. pumping them inside. capturing them with sticky hemolymph.

direct diffusion.

Animals such as jellyfish and cnidarians acquire nutrients and oxygen by: using a trachea system. pumping them inside. capturing them with sticky hemolymph. breathing. direct diffusion.

direct diffusion.

Which organisms are considered deuterostomes? mollusks sponges echinoderms cnidarians arthropods

echinoderms

Birds are ___________________, whereas turtles are _________________. organisms of flight; no longer organisms of flight reptiles; amphibians endotherms; ectotherms ectotherms; endotherms vertebrates; invertebrates

endotherms; ectotherms

Within the animal kingdom, _____ of the 36 phyla contain roughly 99% of all extant animal species. 5 12 9 10 7

9

Animals without backbones represent more than _____ of the total species in the animal kingdom. 95% 50% 1% 25% 10%

95%

Birds are ___________________, whereas turtles are _________________. reptiles; amphibians endotherms; ectotherms organisms of flight; no longer organisms of flight vertebrates; invertebrates ectotherms; endotherms

endotherms; ectotherms

Birds are ___________________, whereas turtles are _________________. vertebrates; invertebrates endotherms; ectotherms organisms of flight; no longer organisms of flight reptiles; amphibians ectotherms; endotherms

endotherms; ectotherms

Which statement about all animals is false? All animals reproduce sexually. All animals are eukaryotes. All animals have a dorsal nerve cord. All animals eat other organisms. All animals are descended from a common ancestor.

All animals have a dorsal nerve cord.

Which statement about animal nervous systems is true? All taxonomic groups of animals have nervous systems, except sponges and jellyfish. All taxonomic groups of animals have nervous systems. All taxonomic groups of animals have nervous systems, except annelids. All taxonomic groups of animals have nervous systems, except sponges. All taxonomic groups of animals have nervous systems, except jellyfish.

All taxonomic groups of animals have nervous systems, except sponges.

Which statement about Charles Darwin's writings on biodiversity and natural selection is true? Darwin hypothesized that lineages that diverged more recently in history are generally more evolved than lineages that diverged earlier in history. Darwin asserted that no creature was more advanced than any other, but each organism was adapted to its particular niche. Darwin hypothesized that brain size and complexity was a relevant approximation of which species was more advanced than another species. Darwin hypothesized that lineages that diverged earlier in history are generally more evolved than more recently diverged lineages. Darwin asserted that the body plan of an organism is the only characteristic that should be considered to determine if the animal is primitive or advanced.

Darwin asserted that no creature was more advanced than any other, but each organism was adapted to its particular niche.

True or false: Animals with backbones are more evolutionarily successful than organisms without backbones. False. Each species exhibits adaptations that best suit their environment. True. This adaptation enables vertebrates to be more successful in their environment. False. This adaptation reduces flexibility and hinders a vertebrate's success in their environment. False. The energy required to produce this structure takes away from vertebrate's ability to reproduce. False. The fact that there is more diversity among invertebrates indicates they are more successful than vertebrates.

False. Each species exhibits adaptations that best suit their environment.

Which type of skeleton contains the carbohydrate called chitin? exoskeleton of insects, crabs, and lobsters endoskeleton of lizards appendicular skeleton of humans hydrostatic skeleton of earthworms fluid skeleton of jellyfish

exoskeleton of insects, crabs, and lobsters

All species are either _____ or _____. evolving; not evolving vertebrates; sponges protected; endangered higher; lower extant; extinct

extant; extinct

Which statement best explains why fins and jaws evolved in a parallel manner? The boney structures in fins are structurally very similar to the teeth found in fish jaws. Fins and jaws are both adaptations for living in water, so they evolved together. Fins and jaws developed from the same mutation and are on the same chromosome. Fins and jaws evolved in a parallel manner just by chance. Fins and jaws work together; fins get you to the organism you are going to eat, and jaws capture and kill it.

Fins and jaws work together; fins get you to the organism you are going to eat, and jaws capture and kill it.

The species of human that averaged only 3 feet tall was: Homo floresiensis. Homo neanderthalensis. Homo habilis. Homo erectus. Homo sapiens.

Homo floresiensis.

Which species most likely gave rise to both Homo neanderthalensis and Homo sapiens? Homo habilis Homo ergaster Homo erectus Homo heidelbergensis Homo floresiensis

Homo heidelbergensis

What is the major developmental characteristic that shows the close relationship between echinoderms and chordates? In both groups, the gut develops from back to front. In both groups, the gut develops from front to back. In both groups, development occurs by continually adding skeletal elements. Both groups are asymmetrical in all life stages. In both groups, all individuals have notochords during the larval stage.

In both groups, the gut develops from back to front.

Which statement about invertebrates is false? Invertebrates are animals without a backbone. Invertebrates are all protostomes. Invertebrates are not a monophyletic group. Invertebrates include arthropods, mollusks, and flatworms, among others. Invertebrates have more species than vertebrates.

Invertebrates are all protostomes.

Which statement about ctenophores is true? Both ctenophores and sponges lack any true tissues. It is possible that the ctenophore nervous system evolved independently from the nervous system found in the common ancestor of all animals except for sponges. Ctenophores predated the ancestral protist from which all animals are descended. Ctenophores cannot have diverged from the rest of the animal kingdom before sponges based on their physiological traits. Ctenophores are a more primitive organism than sponges.

It is possible that the ctenophore nervous system evolved independently from the nervous system found in the common ancestor of all animals except for sponges.

Humans are not a part of which taxonomic group? apes placental mammals Old World monkeys primates animals

Old World monkeys

Which animal phylum lacks true tissues? Annelida (segmented worms) Nematoda (roundworms) Cnidaria (jellies, corals, and their relatives) Platyhelminthes (flatworms) Porifera (sponges)

Porifera (sponges)

Which is NOT a crustacean? barnacles shrimp pill bugs or woodlice crayfish Portuguese man-o'-war

Portuguese man-o'-war

Which statement regarding the differences between reptiles and amphibians is true? Reptiles were the earliest animal group to evolve lungs. Reptiles have amniotic eggs, whereas amphibians do not. Reptiles are less closely related to whales, while amphibians are more closely related to whales. Reptiles are endotherms, while amphibians are ectotherms. Reptiles can't live in water, while all amphibians live in water throughout their lives.

Reptiles have amniotic eggs, whereas amphibians do not.

As mammals evolved, there was a gradual transition from bodies with short legs to bodies with longer legs, held vertically beneath the trunk of the animal. Which was a result of this anatomical change in early mammals? The animals were able to produce milk. Cellular respiration rates decreased. Less heat was generated from the body. Heat was able to be released from under the body. The animals could run faster after prey.

The animals could run faster after prey.

Why are chimpanzees not shown in this figure? Only species that are extinct are depicted in this figure; chimpanzees still exist. The lineage that gave rise to chimpanzees diverged from the lineage that gave rise to humans at an earlier point in time than is depicted here. Humans and chimpanzees do not share any common ancestry; therefore, chimpanzees are not included in this figure. Chimpanzees branched off from the Australopithecus (gracile) lineage; however, because this figure only depicts human history, chimpanzees have been omitted. Humans are not as closely related to chimpanzees as scientists formerly believed.

The lineage that gave rise to chimpanzees diverged from the lineage that gave rise to humans at an earlier point in time than is depicted here.

Which characteristic is unique to vertebrates in the phylum Chordata? The dorsal hollow nerve cord forms what is known as the peripheral nervous system. All vertebrates have a tail, except for humans. The notochord disappears without replacement after the embryonic stage. Nothing is unique about vertebrates because they are the only subphyla of chordates. The notochord is not present throughout life; rather, it is only found in early embryos and is replaced by the vertebral column (backbone).

The notochord is not present throughout life; rather, it is only found in early embryos and is replaced by the vertebral column (backbone).

The phylum Platyhelminthes are more commonly known as: mollusks. snakes. ribbon worms. flatworms. earthworms.

flatworms.

The phylum Platyhelminthes are more commonly known as: snakes. flatworms. mollusks. ribbon worms. earthworms.

flatworms.

Which statement is true of all animals? Animals may be single or multicellular in form. They reproduce asexually. They are capable of movement at some stage of their life cycle. They have sense organs, like eyes and ears. They can sustain themselves exclusively by photosynthesis.

They are capable of movement at some stage of their life cycle.

Which statement is true about starfish, sand dollars, and sea urchins? They all have a distinct head, thorax, and abdomen. They belong to the arachnids. They are radially symmetrical. They are sessile. They have outer skeletons or shells made of chitin.

They are radially symmetrical.

Which statement is true about starfish, sand dollars, and sea urchins? They belong to the arachnids. They are radially symmetrical. They have outer skeletons or shells made of chitin. They are sessile. They all have a distinct head, thorax, and abdomen.

They are radially symmetrical.

All arthropods have: a mantle and a radula. stinging mouthparts. antennae and compound eyes. a chitinous exoskeleton and jointed appendages. six legs and three body segments.

a chitinous exoskeleton and jointed appendages.

A feature that only mammals have is: internal skeleton. a skeleton of calcium carbonate. hair. predatory behavior. bilateral symmetry.

hair.

When thinking about the evolutionary history of humans, which feature is most related to the success of H. sapiens? development of game-playing strategies longer arm length decrease in caloric intake resulting in a lower body weight increase in brain size increased use of teeth as tools

increase in brain size

When thinking about the evolutionary history of humans, which feature is most related to the success of H. sapiens? increased use of teeth as tools increase in brain size development of game-playing strategies decrease in caloric intake resulting in a lower body weight longer arm length

increase in brain size

Most species of animals are: vertebrates. carnivores. autotrophs. radially symmetrical. invertebrates.

invertebrates.

In the phylogeny shown, each species is sorted into its phylum based upon: IMAGE TO INCLUDE: Add figure 13-3 above question stem. how primitive or advanced the species has become. how ancient the most recent common ancestor was, relative to humans. a particular adaptation and whether an ancestor of the species possessed that adaptation. the similarity to human body plans and the major adaptations that define humans. whether the species is currently living or extinct.

a particular adaptation and whether an ancestor of the species possessed that adaptation.

Which anatomical characteristic of humans can be traced back to our arboreal origins? viviparity increased body weight omnivorous diet hair that insulates the body ability to grasp objects with fingers and toes

ability to grasp objects with fingers and toes

Terrestrial vertebrates are classified either as amniotes or non-amniotes. Which of these animals is a non-amniote? amphibians birds reptiles mammals humans

amphibians

Which of these is not a member of the group of vertebrates that produce amniotic eggs? birds monotremes amphibians marsupials whales

amphibians

The most primitive group of animals that had lungs were the: amphibians. ray-finned fish. tunicates. reptiles. birds.

amphibians.

Which trait is unique to arthropods? a ventral nerve cord appendages an exoskeleton growth by molting segmentation

an exoskeleton

The figure represents an evolutionary tree of the: animals. deuterostomes. echinoderms. protostomes. chordates.

animals.

Segmented worms (annelids), roundworms (nematodes), and flatworms (platyhelminthes): are all internal parasites. are all asexual. are all bilaterally symmetrical. are a monophyletic group. are all chordates.

are all bilaterally symmetrical.

Which series of events correctly describes the evolutionary history of the vertebrates, from earliest to latest in time? four limbs, hair, lungs, and jaws four limbs, lungs, jaws, and hair two limbs, lungs, jaws, and hair lungs, jaws, four limbs, and hair jaws, lungs, four limbs, and hair

jaws, lungs, four limbs, and hair

Sharks are to jaws as _____ are to _____. lancelets; notochords manta rays; bony jaws paired fins; tunicates hagfish; swim bladders lampreys; circular oral disks

lampreys; circular oral disks

All of these are arachnids except: ticks. scorpions. lobsters. mites. spiders.

lobsters.

Which is NOT an important feature in distinguishing animals from each other? development of the gut method of locomotion (movement) presence and cellular arrangement of tissues body symmetry growth of skeletal elements

method of locomotion (movement)

In complex chordates, such as vertebrates, the _____ is eventually replaced by a vertebral column. notochord ventral solid nerve cord hollow dorsal nerve cord rigid exoskeleton post-anal tail

notochord

Which terrestrial problem correctly matches its evolutionary solution? oxygen in the air: gills gravity: lungs desiccation: limbs for movement oxygen in the air: lungs gravity: amniotic egg

oxygen in the air: lungs

Which characteristic is unique to lobe-finned fish? swim bladder jaws pelvic and pectoral fins bones filter feeding

pelvic and pectoral fins

In the cnidarians, the two body types are the sessile _____________ and the free-living _______________. coral; anemone anemone; coral zooxanthellae; coral medusa; polyp polyp; medusa

polyp; medusa

In the cnidarians, the two body types are the sessile _____________ and the free-living _______________. polyp; medusa medusa; polyp anemone; coral coral; anemone zooxanthellae; coral

polyp; medusa

In the figure above, the five groups in the green box (including the two in the inner blue box) are all: arthropods. deuterostomes. worms. protostomes. chordates.

protostomes.

The vast majority of invertebrates are: terrestrial. protostomes. parasitic. carnivores. asexually reproductive.

protostomes.

Which term can be associated with gastropods? complete stomach notochord collar cells radula compound eyes

radula

Each group of animals below is paired with a type of body symmetry. Which of these pairings is inaccurate? roundworm; radial symmetry fish; bilateral symmetry mammal; bilateral symmetry cnidaria; radial symmetry sponge; asymmetry

roundworm; radial symmetry

Which groups grow by molting? roundworms and arthropods sponges and cnidarians flatworms, roundworms, and annelids echinoderms and chordates flatworms and mollusks

roundworms and arthropods

Which one of the common names is matched correctly with its phyla? segmented worms: Platyhelminthes tapeworms: Nematoda flatworms: Annelida roundworms: Annelida roundworms: Nematoda

roundworms: Nematoda

Which is an animal with rigid bones, jaws, and a swim bladder? lampreys salmon sharks lobe-finned fish hagfish

salmon

Which organism is an example of an echinoderm? frog ant sand dollar centipede crab

sand dollar

What distinguishes a protostome from a deuterostome? sequence or order of gut development the molting pattern whether the body can be divided into two or more symmetrical units the way the skeleton grows whether an animal has tissues or not

sequence or order of gut development

Which organism does NOT contain chitin? lobsters snails crabs scorpions grasshoppers

snails

The arthropoda class Crustacea includes all of the following kinds of animals except: crayfish. lobsters. crabs. snails. shrimp.

snails.

The arthropoda class Crustacea includes all of the following kinds of animals except: shrimp. lobsters. snails. crabs. crayfish.

snails.

Which group feeds primarily on material filtered from the water? annelids cephalopods gastropods sponges nematodes

sponges

Which is the only animal phylum to not possess true tissues? cnidarians flatworms sponges chordates mollusks

sponges

All groups of animals have nervous systems except: jellyfish. sponges. flatworms. worms. echinoderms.

sponges.

Which is NOT an arthropod? squid shrimp flea louse horseshoe crab

squid

Which organism is not a chordate? tunicate reptile starfish stingray lancelet

starfish

Which type of worms include species that are internal parasites? slugs earthworms leeches polychaetes tapeworms

tapeworms

Reptiles show numerous adaptations for a completely terrestrial life cycle. One adaptation that first occurred in the reptiles includes: the amniotic egg. tetraploidy. lungs. the ability to "breathe" through their skin. teeth.

the amniotic egg.

All animals obtain energy from: stored fatty acids. nutrients within the soil. the consumption of other organisms. inorganic chemical processes. photons originating from the sun.

the consumption of other organisms.

The structure pictured here is: the oral disk of a jawless fish. the cartilaginous skeleton of a stingray. the fin of a ray-finned fish. the fin of a lobe-finned fish. the swim bladder of a finned fish.

the fin of a ray-finned fish.

The lineage that first separated from the common ancestor of all animals, and retains many of the same primitive features to this day, includes which of the following modern organisms? the grasshopper the sponge the sea turtle the earthworm the jellyfish

the sponge

Sponges are sessile organisms as adults. They are classified as animals because: they possess tissues. they grow by molting. their gut forms front to back. they have bilateral symmetry. they exhibit movement as juveniles.

they exhibit movement as juveniles.

The colloquial terms "advanced" and "primitive" when referring to evolution reveal our biases because: those terms are often used to describe the presence or complexity of a nervous system in the different phyla. those terms are often used to describe the complexity of tissues in the different phyla. those terms are often used to describe how similar an organism is to humans, rather than how well adapted it is to its environment. those terms are often used to compare sessile species with various motile species. those terms are often used to describe the species relative to its most recent common ancestor with another species.

those terms are often used to describe how similar an organism is to humans, rather than how well adapted it is to its environment.

All of these are insects except: fleas. lice. flies. bugs. ticks.

ticks.

The undersides of the arms of a sea star are carpeted with ___________________ that extend and contract in waves, grasping and releasing the substrate as the animal glides along. belly feet cnidocytes tube feet radula cilia

tube feet

The undersides of the arms of a sea star are carpeted with ___________________ that extend and contract in waves, grasping and releasing the substrate as the animal glides along. cilia belly feet radula cnidocytes tube feet

tube feet

Which is NOT a characteristic of tunicates? deuterostome free-swimming larvae filter-feeders vertebrae pharyngeal slits

vertebrae

What is the purpose of the adaptation of modified vertebrae in early terrestrial animals? orientation of body in environment protection of young bipedalism withstanding gravity storing calcium

withstanding gravity