The Major Groups of Living Things
On a Saturday at the Yaque del Norte River, Yaritza sees a frog on the bank, a sardine in the cooler at the corner store, and a spider on the wall of her house. They live in different places and move in different ways. How do scientists put so much variety in order? Within each kingdom another level of order is needed: the major groups. This variety of living things is called biological diversity, and the Dominican Republic has a great deal of it.
Vertebrates
When we eat a sardine we find a central backbone, and when we touch our back we feel a row of hard bones. But an earthworm or a jellyfish has a completely soft body. What internal structure divides animals into two major models of organization?
Name the five groups of vertebrates and give an example of an animal for each. Also state the characteristic shared by all vertebrates, which gives the group its name.
Name the five groups of vertebrates and give an example of an animal for each. Also state the characteristic shared by all vertebrates, which gives the group its name.
State which group of vertebrates each animal belongs to and which feature helped you decide: a salmon, a grass snake, an eagle, a toad, and a cow.
State which group of vertebrates each animal belongs to and which feature helped you decide: a salmon, a grass snake, an eagle, a toad, and a cow.
The diagram shows the five groups of vertebrates with a typical trait for each, but one group is missing, marked with "?". State which group it is, describe its defining…
The diagram shows the five groups of vertebrates with a typical trait for each, but one group is missing, marked with "?". State which group it is, describe its defining characteristics, and give two examples of animals from that group.
Explain two differences between amphibians and reptiles (think about the skin and where they lay their eggs) and give an example of each group.
Explain two differences between amphibians and reptiles (think about the skin and where they lay their eggs) and give an example of each group.
Fish, birds, and mammals: adaptations
A fish lives in the water thanks to three traits: the gills take in the oxygen dissolved in the water, the fins let it swim and keep its balance, and its streamlined body (long and smooth) reduces drag in the water.
Birds fly thanks to the feathers of their wings and tail, which provide lift, and to their hollow, lightweight bones, which reduce weight. They lay eggs with a shell.
Mammals have hair, breathe with lungs, and the females have mammary glands. Most are born from the mother's womb. The dolphin and the humpback whale of Samaná Bay are marine mammals: they breathe air and nurse their young. The tuna, on the other hand, is a fish: it breathes with gills and its young hatch from eggs.
Name two characteristics of birds that allow them to fly and briefly explain how each one helps.
Name two characteristics of birds that allow them to fly and briefly explain how each one helps.
Fish are adapted to life in water. Explain the role of the gills, the fins, and the streamlined body shape.
Fish are adapted to life in water. Explain the role of the gills, the fins, and the streamlined body shape.
Compare a dolphin with a tuna: state which group each belongs to and explain two differences between them, thinking about how they breathe and how their young are born…
Compare a dolphin with a tuna: state which group each belongs to and explain two differences between them, thinking about how they breathe and how their young are born and fed.
Create a table with three columns —group, main feature, and example— and fill it in for these six groups of living things: fish, amphibians, reptiles, birds, mammals,…
Create a table with three columns —group, main feature, and example— and fill it in for these six groups of living things: fish, amphibians, reptiles, birds, mammals, and insects.
A classmate makes the following statement: "Since sharks have a skeleton made of cartilage rather than true bone, they should be classified as invertebrates, just like…
A classmate makes the following statement: "Since sharks have a skeleton made of cartilage rather than true bone, they should be classified as invertebrates, just like squids or crabs." Refute their stance by pointing out two fundamental differences between the internal skeleton of a shark and the protective coverings or shells of invertebrates, and explain what unique internal structure places the shark within the vertebrate group.
Invertebrates
Explain what an invertebrate is and name four groups of invertebrates with an example of an animal from each.
Explain what an invertebrate is and name four groups of invertebrates with an example of an animal from each.
How many legs do insects have and how many do arachnids have? Name two animals from each group and point out another visible difference between them.
How many legs do insects have and how many do arachnids have? Name two animals from each group and point out another visible difference between them.
From this list of animals —dog, ant, spider, earthworm, snail, jellyfish, and trout— first separate the vertebrates from the invertebrates. Then, group the invertebrates…
From this list of animals —dog, ant, spider, earthworm, snail, jellyfish, and trout— first separate the vertebrates from the invertebrates. Then, group the invertebrates into insects, arachnids, worms, molluscs, and jellyfish, stating a feature that helped you decide in each case.
Classify these invertebrates into their group (insect, arachnid, mollusc, crustacean, worm, or other) and justify each choice with a feature: a scorpion, a mussel, a…
Classify these invertebrates into their group (insect, arachnid, mollusc, crustacean, worm, or other) and justify each choice with a feature: a scorpion, a mussel, a centipede, a prawn, and a sponge.
The metamorphosis of insects
Many insects change shape as they grow: this is metamorphosis. The butterfly goes through egg, caterpillar, chrysalis, and adult. The caterpillar chews leaves; the adult sips nectar with a proboscis. Because they eat different things, the caterpillar and the adult do not compete with each other, and the adult also pollinates flowers.
During a field trip, a group of students collected four unidentified invertebrates: Specimen A: soft, unsegmented body, protected by a spiral shell. Specimen B: body…
During a field trip, a group of students collected four unidentified invertebrates:
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Specimen A: soft, unsegmented body, protected by a spiral shell.
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Specimen B: body divided into head, thorax, and abdomen, with 6 legs and a pair of antennae.
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Specimen C: body divided into cephalothorax and abdomen, with 8 legs and no antennae.
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Specimen D: cylindrical body divided into repeated rings, with no legs and moist skin.
Design a simple dichotomous key (based on successive "yes / no" questions about observable traits) that allows anyone to unequivocally identify which group (insects, arachnids, annelids, or gastropods) each specimen belongs to.
In a school garden, a pest of caterpillars appears, voraciously devouring lettuce leaves. Weeks later, the caterpillars form chrysalises and transform into adult…
In a school garden, a pest of caterpillars appears, voraciously devouring lettuce leaves. Weeks later, the caterpillars form chrysalises and transform into adult butterflies that only drink nectar from flowers. A student states: "Metamorphosis is a disadvantage for the butterfly because the caterpillar and the adult compete with each other for food." Refute the student's statement by explaining what ecological advantage is provided by the radical change in diet and mouthparts between both stages, and predict what consequences the total elimination of the adults would have for the flowering plants in the garden.
Plant groups
Mosses have no true roots or conducting vessels; they grow in damp, shady places, on rocks and tree trunks. Ferns have roots, stems, and leaves, but no seeds; they are abundant in humid, cloudy forests. Both reproduce by means of spores, and their fertilization depends on liquid water.
Seed plants include the gymnosperms, such as the Hispaniolan pine of the Cordillera Central, whose seeds are not enclosed in fruits, and the angiosperms, such as the mango, the avocado, or the geranium, with flowers and seeds inside fruits. Pine cones are not fruits.
The parts of a flowering plant
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Root: anchors the plant to the soil and absorbs water and mineral salts.
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Stem: supports the plant and carries water and nutrients.
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Leaves: carry out photosynthesis, with which the plant makes its food.
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Flower: is the reproductive organ; after fertilization it forms the fruit.
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Fruit: protects the seeds and helps disperse them.
State which group each of these living things belongs to and justify each answer with a feature of the corresponding group: a frog, a sardine, a cat, a spider, a fern,…
State which group each of these living things belongs to and justify each answer with a feature of the corresponding group: a frog, a sardine, a cat, a spider, a fern, and a geranium.
Explain the difference between mosses, ferns, and flowering plants, and give an example of each group that you could find near where you live. What type of habitat does…
Explain the difference between mosses, ferns, and flowering plants, and give an example of each group that you could find near where you live. What type of habitat does each typically grow in?
Name the main parts of a flowering plant (root, stem, leaves, flower, and fruit) and explain the function of each one.
Name the main parts of a flowering plant (root, stem, leaves, flower, and fruit) and explain the function of each one.
A botanical study compares two slopes of a mountain: the north-facing slope is permanently shaded and moist due to constant dew, while the south-facing slope is dry,…
A botanical study compares two slopes of a mountain: the north-facing slope is permanently shaded and moist due to constant dew, while the south-facing slope is dry, sunny, and receives sparse, concentrated rainfall. On the north-facing slope, mosses and ferns thrive, whereas on the south-facing slope, only seed plants (pines and rockroses) manage to survive. Justify this distribution of vegetation by explaining why ferns need liquid water to complete their reproduction and which two structures (related to reproduction) enable seed plants to conquer dry environments.
Classify by relationship, not by where they live
The kingdoms, once again
Organisms are also grouped by their cell type, their number of cells, and their nutrition. A unicellular, eukaryotic organism with chloroplasts that makes its own food is a protist (alga). A multicellular, heterotrophic one that absorbs its food and has a cell wall, without true tissues, is a fungus. A sponge, multicellular, heterotrophic by ingestion and without differentiated tissues, is an animal, even though it lives attached to a rock.
The sea urchin is named after the hedgehog ("urchin" is an old word for it), but one is a marine invertebrate and the other a mammal. Explain what this case shows about…
The sea urchin is named after the hedgehog ("urchin" is an old word for it), but one is a marine invertebrate and the other a mammal. Explain what this case shows about the common names of animals and compare the characteristics of both.
An explorer finds an unknown marine animal: it has a streamlined body, lacks hind limbs, moves by means of flippers, and spends its entire life underwater. However, he…
An explorer finds an unknown marine animal: it has a streamlined body, lacks hind limbs, moves by means of flippers, and spends its entire life underwater. However, he observes that it periodically surfaces to take in air and that it gives birth to live young which it feeds with milk. The explorer notes in his journal: "Because of its shape and because it always lives in water, it is a new species of fish." Refute his conclusion by justifying why it should be classified as a mammal, and predict what type of reproduction, fertilisation, and thermal regulation (homeothermic or poikilothermic) you would expect to find in this animal.
In a school laboratory, three unknown organisms are analysed and their cellular and nutritional characteristics are recorded: Organism A: unicellular, eukaryotic, with…
In a school laboratory, three unknown organisms are analysed and their cellular and nutritional characteristics are recorded:
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Organism A: unicellular, eukaryotic, with chloroplasts and autotrophic nutrition.
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Organism B: multicellular, heterotrophic by absorption, with a cell wall and lacking true tissues.
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Organism C: multicellular, heterotrophic that ingests food, lives attached to a marine rock, and lacks differentiated tissues.
Determine with reasoning which kingdom each organism belongs to based on its cellular and nutritional data. In addition, explain why organism C belongs to the animal kingdom despite living immobile like a plant.
Look at these three animals: the bat, the sparrow, and the dolphin. If we used a classification criterion based exclusively on the medium through which they move, which…
Look at these three animals: the bat, the sparrow, and the dolphin. If we used a classification criterion based exclusively on the medium through which they move, which two animals would you group together? Explain why this criterion is misleading for biologists and justify, by comparing the internal anatomy of their limbs and their mode of reproduction, why the bat is much more closely related to the dolphin than to the sparrow.
We protect what we know
The Dominican Republic has unique animals, such as the solenodon (a mammal), the Palmchat (a bird), the rhinoceros iguana (a reptile), and the manatee (a marine mammal). Knowing which group they belong to and which traits they have helps us understand why they must be protected. When researching, look in reliable sources, such as the Ministry of Environment and Natural Resources, the National Botanical Garden, or the National Museum of Natural History, and cite them.
In a stretch of a river, two protected species live together: the brown trout (a fish with branchial respiration) and the Pyrenean desman (a small semiaquatic mammal…
In a stretch of a river, two protected species live together: the brown trout (a fish with branchial respiration) and the Pyrenean desman (a small semiaquatic mammal that dives to hunt larvae). Due to a chemical spill, dissolved oxygen in the water drops to levels close to zero for several weeks, while the water surface and the outside air remain unchanged. Predict, with reasoning, which of the two species will suffer immediate mortality from suffocation and which will better resist the drop in dissolved oxygen, justifying your answer based on their respiratory mechanisms.
Back to the beginning: the sardine (fish) and the frog (amphibian) are vertebrates because they have a backbone; the spider is an invertebrate (an arachnid) with eight legs. The group is defined by relationship and body traits, not by where they live or how they move.